UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


WATER-POWER, 


AN   OUTLINE    OF   THE   DEVELOPMENT  AND 

APPLICATION   OF   THE  ENERGY 

OF  FLOWING    WATER. 


JOSEPH    P.     FRIZELL, 

HYDRAULIC  ENGINEER, 

Member  of  the  American  Society  of  Civil  Engineers, 
Member  of  the  Boston  Societv  of  CM!   Engineers. 


FIRST   EDITION. 
FIRST    THOUSAND. 


NEW   YORK: 

JOHN   WILEY   &   SONS. 

LONDON:    CHAPMAN  &   HALL,   LIMITED. 

1901. 


JOSEPH    P.   FRIZELL. 


ROBERT  DRUMMOND,    PRINTHR,   NEW  YORK. 


TC 

m 

P?/w 


PREFACE. 


WATER-POWER,  which  was  formerly  the  chief  reliance  of 
mankind  in  industry,  has  been  greatly  overshadowed  in  recent 
times  by  the  cheapness  of  coal  and  the  development  of  the 
steam-engine.  This"  condition,  while  permanent  to  all  imme- 
diate practical  intents,  is  nevertheless,  upon  a  broad  view  of 
the  subject,  merely  temporary.  Two  hundred  and  fifty  years 
ago,  when  unbroken  forests  stretched  from  the  Penobscot  to 
the  W abash,  the  idea  of  a  scarcity  of  wood  and  timber  appeared 
grotesque.  At  the  present  day,  the  idea  of  the  exhaustion  of 
existing  deposits  of  coal  appears  equally  so.  Nevertheless 
that  time  will  certainly  come.  Our  deposits  of  coal  are  finite; 
every  ton  taken  from  the  mines  leaves  a  ton  less  to  be  mined. 
Coal  does  not  have  the  power  of  reproduction  even  to  the 
extent  that  wood  and  timber  have.  It  does  not,  like  water, 
have  the  power  of  rising  in  the  form  of  vapor  after  having 
developed  energy  by  descending.  Coal  deposits  are  simply 
an  enormous  store  of  fuel  in  rapid  process  of  destruction  by 
fire.  Water,  on  the  other  hand,  will  continue  to  stand  man- 
kind in  good  stead  long  after  the  reluctant  earth  has  yielded 
up  its  last  ton  of  coal ;  at  least,  long  after  coal  has  become  too 
inaccessible  and  consequently  too  expensive  to  be  used  for 
power. 

Recent  remarkable  developments  in  electricity  and  other 
modes  of  transmitting  mechanical  energy  have  recalled  water- 
power  to  something  like  its  former  position  in  industrial 
economy.  Whereas  formerly  it  was  necessary  that  the  in- 

iii 

210939 


CONTENTS. 


CHAPTER  PACK 

I.  NATURAL  WATERCOURSES i 

II.  DAMS  FOR  WATER-POWER 15 

III.  CONSTRUCTION  OF  DAMS 40 

IV.  DAMS   OF  MASONRY 93 

V.  APENDAGES  OF  DAMS 116 

VI.  MOVABLE  DAMS 133 

VII.  STORAGE-RESERVOIRS  AND    RESERVOIR-DAMS* 145 

VIII.  ROCK-FILL  DAMS 164 

IX.  RESERVOIR-DAMS   OF  MASONRY 175 

X.  EXAMPLES   OF  HIGH  DAMS 189 

XI.  FAILURES  OF   HIGH  DAMS 204 

XII.  CANALS,  GATES,  ETC 224 

XIII.  HYDRAULIC  MOTORS.    WATER-WHEELS 241 

XIV.  TURBINES 266 

XV.  APPENDAGES  AND  ATTACHMENTS  OF  TURBINES 306 

XVI.  CANALS 348 

XVII.  DEVELOPMENT  OF  NATURAL  WATER-POWERS 364 

XVIII.  TRANSMISSION  OF  POWER.     SHAFTING  AND  WIRE  ROPE....  379 

XIX.  HYDRAULIC  TRANSMISSION 397 

XX.  TRANSMISSION  BY  COMPRESSED  AIR 411 

XXI.  TRANSMISSION  BY  ELECTRIC  CURRENT 429 

XXII.  THR   POWER-HOUSE 443 

XXVIII.  MEASUREMENT  OF  WATER 478 

XXIV.  STORAGE  AND  PONDAGE  OF  WATER 514 

XXV.  DAMAGES  TO  MILL-OWNERS  RESULTING   FROM   THE   DIVER- 
SION OF  WATER 549 

vii 


WATER-POWER. 


CHAPTER   I. 
.NATURAL  WATERCOURSES. 

PHYSICISTS  are  wont  to  assert  that  the  sun  is  the  source  of 
all  power  upon  the  earth.  It  creates  fuel  by  separating  carbon 
from  the  carbonic  acid  of  the  atmosphere  and  storing  it  in  the 
substance  of  plants.  In  former  times,  when  this  constituent 
of  the  atmosphere  was  much  more  abundant  than  at  present, 
it  thus  originated  the  vast  accumulations  of  vegetable  growth 
which  now  constitute  the  coal-mines.  By  rarefying  parts  of 
the  atmosphere  and  disturbing  the  barometric  equilibrium,  it 
creates  the  winds,  which  involve  enormous  power.  A  current 
of  air  one  mile  wide,  100  feet  high,  and  moving  with  the 
moderate  velocity  of  30  miles  an  hour  represents  an  expendi- 
ture of  more  than  100000  horse-power.  The  sun  creates  the 
food  which  nourishes  animals  and  gives  them  the  strength  to 
perform  labor.  It  also  sets  in  motion  the  agencies  which  give 
rise  to  water-power. 

Watercourses. — About  three-fourths  of  the  earth's  surface 
is  water,  from  which  evaporation  is  constantly  going  on. 
Water  in  the  form  of  vapor  is  constantly  rising  from  the  seas. 
It  is  distributed  by  the  winds  in  very  unequal  measure  through- 
out the  land,  falls  in  the  form  of  rain  or  of  snow  which  resumes 
the  liquid  form,  and,  gathering  into  streams,  pursues  its  course 


2  NATURAL    WATERCOURSES. 

toward  the  sea.  Rivers  owe  their  existence  to  this  ceaseless 
play  of  natural  forces,  and  to  the  further  fact  that  the  contrac- 
tion of  the  earth's  crust  has  tended  to  form  its  surface  in  a 
series  of  ridges  and  valleys. 

Flow  of  Streams. — The  agencies  which  sustain  the  flow  of 
streams  are  of  extremely  variable  and  intermittent  character, 
whence  arises  great  variation  in  the  flow  of  streams.  No  feature 
of  streams  is  more  striking  than  this.  Rivers  as  large  as  the 
Connecticut  at  Hartford,  with  a  drainage-ground  of  IOOOO 
square  miles,  carry  forty  times  as  much  water  at  one  time  as 
another.  The  maximum  flow  of  the  Merrimac  at  Lowell, 
where  its  drainage-area  is  some  4000  square  miles,  is  sixty  or 
seventy  times  the  minimum.  The  Kanawha  River  at  Charles- 
ton, W.  Va.,  with  a  drainage-area  of  9000  square  miles,  has 
varied  in  the  ratio  of  one  to  one  hundred.  The  Minnesota 
River  at  Fort  Snelling,  Minn.,  draining  some  16000  square 
miles,  has  been  known  to  carry  8  or  10  cubic  feet  per  second 
for  every  square  mile  of  its  drainage-area;  at  other  times, 
not  over  i  cubic  foot  per  second  to  every  30  square  miles.  In. 
small  streams  draining  10  square  miles  and  under,  the  varia- 
tions are  almost  without  limit.  The  extent  of  the  drainage- 
area  together  with  the  rainfall  of  the  region  forms  the  most 
reliable  indication  of  the  flow  of  a  stream  both  in  flood  and  low 
water. 

The  Slope  of  a  stream  or  fall  .per  mile,  together  with  the 
quantity  of  water  to  be  relied  on,  determines,  its  value  for  water- 
power.  Nearly  all  the  streams  emptying  into  the  Atlantic  and 
the  Gulf,  except  the  Mississippi  and  its  lower  tributaries,  have 
some  points  of  resemblance  in  respect  to  slope.  From  the 
point  where  they  are  large  enough  to  be  regarded  as  rivers  to 
where  the  influence  of  the  tide  becomes  apparent,  they  have  a 
fall  of  from  2  to  10  feet  per  mile.  The  slope  is  greatest  in  the 
upper  reaches  of  the  stream,  and  diminishes  toward  tide-water. 
It  is  by  no  means  uniform.  Shoals  and  rapids  occur,  often 
many  miles  in  extent,  with  a  fall  much  above  the  average, 
and  stretches  of  quiet  water  with  a  fall  much  below. 


STREAMS  IN  DIFFERENT  SECTIONS.  3 

Streams  in  Different  Sections  of  the  United  States.— In 
other  respects  there  is  a  material  difference  between  the 
streams  of  the  Northern  and  those  of  the  Southern  States.  This 
difference  arises  from  three  causes,  viz.  :  I .  The  effect  of 
glacial  action,  occasioning  great  deposits  of  drift  over  the 
Northern  and  especially  the  Northeastern  section  which  are 
wanting  at  the  south.  2.  The  greater  effects  of  volcanic  action 
in  the  former.  3.  The  difference  in  climate.  From  the  first 
of  these  causes  it  results  that  Northern  rivers  flow  in  beds  of 
gravel  and  boulders,  with  valleys  sloping  gently  upward  from 
the  stream,  while  Southern  rivers  flow  mainly  in  canyons  or 
trenches  worn  out  of  the  original  rock  with  nearly  vertical 
escarpments,  and  often  partly  filled  with  alluvial  deposits.  To 
glacial  action  is  also  due  the  immense  number  of  lakes  which 
dot  the  surface  of  the  Northern  section,  and  exert  a  marked 
influence  on  the  flow  of  streams,  a  feature  entirely  wanting  at 
the  South.  To  the  second  cause  is  due  the  prevalence  of 
metamorphic  rocks  in  the  Northern  section  which  by  their 
upheaval  have  created  so  many  falls  and  rapids,  and  by  their 
great  hardness  defy  the  abrasive  action  of  the  water.  The 
Southern  river-beds  usually  lie  in  sedimentary  rocks  of  nearly 
horizontal  stratification  and  often  very  fragile  structure.  In  the 
third  place  the  heat  is  more  intense  in  the  Southern  States,  the 
hot  weather  of  longer  duration,  and  in  the  Southwestern  part 
the  rainfall  is  less.  Little  snow  falls  and  no  ice  accumulates. 
The  rains,  when  they  do  come,  are  more  violent.  These 
causes,  together  with  the  absence  of  any  regulating  effect  of 
lakes  or  great  bodies  of  drift,  tend  decidedly  to  increase  the 
fluctuations  of  streams,  diminishing  the  low-water  flow  and 
increasing  the  floods.  In  some  streams  of  the  extreme  South- 
west the  variations  of  flow  are  literally  infinite,  their  beds  being 
dry  at  times  and  roaring  torrents  at  others.  • 

In  regions  where  snow  accumulates,  streams  flowing  east  or 
west,  like  the  Ohio,  the  Missouri,  or  the  Minnesota,  are  liable 
to  severer  floods  than  streams  flowing  south,  like  the  Connecti- 
cut, the  Hudson,  and  the  Upper  Mississippi.  In  the  first,  the 


4  NATURAL    WATERCOURSES. 

melting  takes  place  simultaneously  along  its  course,  and  the 
water  is  all  precipitated  into  the  channel.  In  the  latter,  the 
melting  extends  slowly  up  the  stream,  the  result  of  one  day's 
melting  being  well  on  its  way  before  the  next  day's  contribu- 
tion enters  the  channel.  Streams  flowing  in  a  northerly  direc- 
tion, like  the  Red  River  of  the  North  and  some  of  the 
tributaries  of  the  St.  Lawrence,  are  subject  to  great  floods 
during  the  breaking  up  of  the  ice,  which  commences  at  the 
head  of  the  stream  and  moves  northward,  constantly  encounter- 
ing firmer  ice.  The  ice  accumulates  in  immense  masses,  jams 
and  dams  the  water,  which  is  all  the  time  increasing  from  the 
melting  of  snow.  On  the  Red  River  of  the  North  it  is  no 
uncommon  thing  to  see  driftwood  among  the  branches  of  trees 
40  feet  above  the  ground.  Such  conditions  are  very  trying  to 
any  artificial  structure  placed  in  the  river. 

In  the  Northeastern  section,  in  the  latitude  of  Boston,  the 
total  volume  of  water  carried  annually  by  streams  is  distributed 
throughout  the  year  very  much  as  follows : 

January.. .  .  10  per  cent.  July 2  per  cent. 

February..   14        "  August 3 

March .  ...  20       "  September.  .3        " 

April 15        "  October 5 

May 10       "  November..  6 

June 4       «  December.. .  8 

In  the  Mississippi  valley,  in  the  same  latitude,  this  proportion 
is  changed  by  a  different  distribution  of  the  rainfall.  In  the 
extreme  North,  the  lowest  water  occurs  in  the  winter,  the  tem- 
perature remaining  below  freezing,  often  for  months  in  succes- 
sion, during  which  time  no  water  enters  the  streams  except 
from  springs.  The  extremely  low  stage  of  the  Minnesota 
above  referred  to  occurred  in  the  winter,  after  a  long  period  of 
extremely  cold  weather.  In  the  South  Atlantic  and  Gulf 
States  there  is  no  snow  to  affect  the  spring  flow.  The  streams 
are  usually  high  during  the  winter  and  become  very  low  during 
the  latter  part  of  the  summer  and  autumn.  In  Texas  and  New 


RELATION  OF  SLOPE,  DEPTH,  AND    VELOCITY.  5 

Mexico  the  normal  flow  of  the  streams  is  maintained  by- 
springs,  the  result  of  rainfall  in  previous  years.  The  drainage- 
areas  being  vastly  greater  than  for  streams  of  equal  flow  in 
other  sections,  a  concurrence  of  rains  in  all  the  tributaries  gives 
rise  to  an  enormous  flood,  which  comes  down  with  the  velocity 
of  a  bursting  reservoir  or  a  tidal  bore.  It  subsides  rapidly  and 
the  river  very  soon  returns  to  its  normal  condition. 

Nearly  one-half  the  territory  of  the  United  States,  called 
the  Arid  Region,  comprising  the  entire  area  west  of  the  looth 
meridian  except  the  narrow  margin  between  the  Pacific  Ocean 
and  the  Coast  Range,  is  a  region  deficient  in  water,  the  rainfall 
ranging  from  6  inches  per  annum  in  Nevada  to  30  inches  in 
other  parts.  The  entire  State  of  Nevada  and  a  part  of  Utah  lie 
in  a  basin  which  has  no  drainage  to  the  sea,  all  the  water  that 
falls  upon  it  being  removed  by  evaporation.  In  many  parts  of 
the  Arid  Region  no  agricultural  production  is  possible  without 
artificial  irrigation,  and  in  no  part  of  it  can  agriculture  be 
carried  on  with  full  success  without  this  aid.  The  interests  of 
irrigation  on  all  the  streams  are  held  to  be  paramount  to  those 
of  water-power,  and  the  latter  thus  becomes  of  quite  secondary 
importance  throughout  this  part  of  the  country. 

Table  I  gives  some  facts  of  interest  in  regard  to  the  flow 
of  streams  in  different  parts  of  the  United  States.  It  is  taken 
from  vol.  1 6  of  the  roth  United  States  Census  Report,  and 
from  the  1 8th  Annual  Report  of  the  U.  S.  Geological  Survey. 

Relation  of  Slope,  Depth,  and  Velocity  in  Streams. — If  we 
carefully  determine,  by  levelling,  the  fall  in  a  given  length  of  a 
running  stream,  and  divide  the  fall  expressed  in  feet  by  the 
length  in  feet,  this  quotient  is  called  the  slope  and  is  repre- 
sented by  the  letter  5.  Suppose  the  length  to  be  a  mile,  and 

the  fall   2   feet,    the  slope  is   -^  =  0.000379.      Let  Fig.    I 

represent  the  cross-section  of  a  river-channel,  ab  the  surface, 
acdb  the  bottom.  Measure  the  depth  at  a  number  of  equidis- 
tant points;  the  average  of  these  measurements  is  the  mean 
depth.  Measure  also  the  velocity  at  a  number  of  equidistant 


NATURAL    WATERCOURSES. 


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RELATION  OF  SLOPE,  DEPTH,  AND    VELOCITY.  7 

points  by  methods  to  be  hereafter  explained,  and  thus  deter- 
mine the  mean  velocity,  which  is  designated  by  v.  Determine 
the  length  acdb  of  the  line  representing  the  bottom.  This 


FIG.  i. 

length  is  called  the  "wetted  perimeter."  The  mean  depth 
multiplied  by  the  width  ab  is  the  area  of  the  cross-section. 
This  area,  divided  by  the  wetted  perimeter,  is  called  the 
"  hydraulic  mean  depth  "  or  the  "  mean  radius,"  and  is  repre- 
sented by  R.  It  is  obvious  that  in  a  natural  river-channel  the 
wetted  perimeter  is  not  materially  different  from  the  width, 
and  that  no  great  error  can  result  from  taking  the  one  equal  to 
the  other.  In  an  artificial  canal  with  vertical  side"  walls, 
Fig.  2,  the  wetted  perimeter  may  differ  very  materially  from 


FIG.  2. ' 

the    width.       The    relation    between    the    slope,    depth,    and 
velocity,  in  a  stream,  is  ordinarily  expressed  by  the  formula 


Though  this  is  the  best  formula  that  modern  hydraulic  science 
has  to  offer  for  the  case  in  hand,  it  is  still  very  imperfect. 
The  factor  c  varies  between  such  wide  limits  that  no  general 
value  can  be  assigned  to  it.  It  is  not  only  different  for  different 
streams  and  for  different  localities  on  the  same  stream,  but  it 
varies  for  the  same  locality  at  different  stages  of  the  stream, 


8  NATURAL    WATERCOURSES. 

which  shows  that  it  does  not  truly  express  the  law  of  the 
phenomenon.  Nevertheless,  in  default  of  a  better  expression, 
we  have  to  make  such  use  as  we  can  of  it.  The  only  rational 
use  that  the  writer  is  able  to  make  of  it  is  by  the  aid  of  a  table 
of  data  contained  in  the  work  of  Ganguillet  and  Kutter,  trans- 
lated by  Trautwine  and  Hering.  This  contains  results  of 
measurements  by  different  experimenters  on  a  great  number 
of  streams  and  channels  from  which  it  is  usually  possible  to 
select  the  value  of  c  suited  to  the  case  we  have  in  view. 

For  rivers  and  canals  with  fairly  regular  channels  in  earth,, 
with  values  of  R  less  than  0.5    c  may  be  30 ; 
from  0.5  to    i  "         45; 

"i       "2  "         55; 

„     2      «     3          «         65; 

"     3       "     4          »         80; 
"     4      "  10          "       100. 

On  great  rivers,  when  R  is  from  30  to  75  c  may  run  from  125 
to  275. 

Flowage  Occasioned  by  Dams. — Questions  as  to  the  extent 
to  which  the  surface  of  a  stream  is  raised  by  a  dam  are  of  very 
frequent  occurrence.  Such  questions  as  to  an  existing  dam 
can  be  best  determined  by  levelling.  It  is  often  required, 
however,  to  find  how  far  the  flowage  of  a  proposed  dam  will 
extend,  which  can  only  be  determined  by  calculation.  Even 
in  that  case  a  survey  of  the  river-channel  would  be  made  and 
numerous  cross-sections  taken  of  the  stream  and  valley.  In 
endeavoring  to  elucidate  the  principles  of  the  case,  with  no 
existing  data,  we  must  proceed  upon  mere  supposition  as  to 
the  contour  of  the  ground. 

We  will  assume  a  stream  100  feet  wide,  a  maximum  depth 
of  6  feet,  and  a  mean  depth  of  4  feet,  the  area  of  cross-section 
being  400  square  feet.  Suppose  the  fall  to  be  2  feet  per  mile 
and  the  mean  velocity  3  feet  per  second,  which  would  make 
s  =  0.000379  and  would  imply  a  value  of  77  for  c,  the  relation 
of  slope,  velocity,  etc.,  being  expressed  by  the  formula 

v  =  77  VRS. 


FLO  WAGE   OCCASIONED   BY  DAMS.  9 

We  will  assume  a  parabolic  cross-section  for  the  valley  in 
which  the  river  flows,  a  supposition  which  ordinarily  represents 
the  facts  reasonably  well.  The  equation  of  the  parabola  is 
j3  =  2.Px,  where  x  and  y  are  the  coordinates  of  any  point  in 
the  curve,  x  being,  in  this  case,  the  maximum  depth,  and  y  the 
semi-width.  We  have  the  relation  5O2  =  2.P  X  6,  so  that 

2P  =  —£—  =  417,  and  when  the  water  rises,  the  relation 
between  depth  and  width  will  be  expressed  by 

(semi- width)2  =  417  X  max.  depth.        .      .      (2) 

That  is  to  say,  for  purposes  of  computation  we  may  put  the 
width  of  the  stream  as  raised  by  a  dam  equal  to 


2  474I7  X  max.  depth  =  40.8  I/max,  depth. 

We  neglect  the  small  error  that  results  from  assuming  the 
width  equal  to  the  wetted  perimeter,  which  allows  us  to  put  R 
equal  to  two-thirds  the  maximum  depth. 

Now  suppose  the  surface  of  the  stream  to  be  raised  12  feet 
by  a  dam.  If  the  water  in  the  pond  stood  at  an  exact  level, 
the  flowage  would  extend  6  miles  up  the  stream.  This  point 
where  the  natural  surface  of  the  stream  is  at  the  same  level  as 
the  water  at  the  dam  is  called  the  hydrostatic  limit  of  the 
flowage,  and  its  distance  from  the  dam  is  called  the  hydrostatic 
amplitude.  The  surface  of  water,  however,  cannot  be  at  an 
exact  level  while  it  is  in  motion.  The  water  in  the  pond  is 
moving,  very  slowly  near  the  dam,  more  rapidly  further  up. 
Some  head  is  required  to  maintain  the  movement,  and  the 
stream  will  be  somewhat  raised  at  the  hydrostatic  limit.  The 
velocity  increases  and  the  depth  diminishes  as  we  go  up  the 
stream,  so  that  no  formula  can  apply  to  the  entire  reach  under 
consideration.  The  best  we  can  do  is  to  divide  the  channel 
into  lengths  such  that  the  velocity  and  depth  can,  without 
serious  error,  be  regarded  as  constant  in  each,  and  compute 
the  slope  for  each  length.  For  an  approximate  computation 


IO  NATURAL    WAl^ERCOURSES. 

we  will  take  lengths  of  a  mile  each,  and  will   consider  the 
cross-section  and  velocity  at  the  middle  of  each  mile  section. 

At  a  distance  of  half  a  mile  up-stream  from  the  dam,  we 
should  have  the  maximum  depth  6  -f-  12  —  i  =  17  feet. 
The  mean  depth  we  take  at  two  thirds  the  maximum,  viz., 
11.333,  and  this  is  approximately  equal  to  R.  The  width  is 
40.8  Viy  =  168.3.  For  the  increased  depth  we  must  adopt  a 
higher  value  of  c,  say  c  =  105.  The  cross-section  is  11.333 

X   168.3  =  *  907-4>  and    the    velocity  =  -        ; — -  =  0.629. 
We  have  therefore  for  the  fall  in  the  first  mile 

5280,  =  5»8o9)'         =  0.0,67,  feet. 


For  the  second  mile  we  have  the  depth  i£  miles  above  the 
dam  12  +  6  —  3  =  15,  R  =  10,  width  =  40.8  VT$  =158, 
cross-section  =  1580,  velocity  =  — —  —  0.760.  We  may 
take  c  =  100.  We  have  therefore  for  the  fall  in  the  second  mile 

5280*  =  5280— 2^-.=L-a  =  0.03050. 
10  x  100 

For  the  third  mile  we  have  the  max.  depth  =12  +  6—5 
=  13,  R=  8.67,  width  =  40.8  vTs  =  147.  ii,  cross-section 
=  1275.  In  this  section  the  slope  of  the  surface  sensibly 
affects  the  cross-section. 

We  have  for  the  fall  in  the  first  mile o  0167 

Second  mile '.'  0*0305 

Estimated  in  half  the  third  mile 0.0300 

Total  ~ 

Correction  for  the  cross-section  0.0772  X  147.11  =  n.36 
Making  the  corrected  cross-section  1286.36, 

1 200 
velocity  =  I2g6        =  0.933.      We  take  c  =  95. 


FLO  WAGE   OCCASIONED   BY  DAMS. 


CO. 

Fall  in  third  mile  =  5280,    \,       o  ^    =  0.0587. 
(95)2  X  8.67 

For  the  fourth  mile  we  have  max.  depth  at  3^  miles 

1  2  -f-  6  —  7  =  ............................  ii.  ooco 

Add  fall  in  first,  second,  and  third  miles  and  half  of 
fourth,  estimated  at  0.06 


Corrected  max.  depth  ..............  ............     11.1659 


Mean     depth  =  R  =  7.444,     width  =  40.8  4/11.1659  = 
>.3,   cross-section  = 
We  may  take  c  =  90. 


1200 

136.3,   cross-section  =  1014.62,  velocity  =  —    — ^-  =  1.183. 

1014-  62 


Fall  in  fourth  mile  =  5280^^^  =  0.1225. 

For  the  fifth  mile  we  have  for  the  max.  depth 

12+6  —  9  = 9.0000 

Add  fall  in  first,  second,  third,  fourth,  and  half  of  fall 

in  fifth,  estimated  at  o.  1450 O-  3734 

Corrected  max.  depth 9-3734 


R  =  6.249,  width  =  40.8  1/9.3734  =  124.91,  cross-section 
=  780.58,  c  =  86,  velocity  =  =  1-537- 


Fall  in  fifth  mile  =  jagogjg  =  0.2700. 

For  the  sixth  mile  max.  depth  —  7.8188,  R  =  5.213,  width 
=  40.81/7.8188=114.09,    cross-section  =  594.73,    velocity 
1200 


=  2.018,  c  may  be  taken  at  81. 


594-73 

Fall  in  sixth  mile  =  528o77r~r — ~- =  0.6285. 

(Si)2  X  5-213 


12  NATURAL    WATERCOURSES. 

Collecting  these  several  quantities  we  have : 

Fall  in  first  mile 0.0167 

"    "  second  " 0.0305 

"    "  third       " 0.0587 

"    "  fourth    " 0.1225 

"    "fifth        " 0.2700 

"    "sixth      " 0.6285 

At  the  hydrostatic  limit  the  water  is  raised .  .    1 .  1 269 

To  pursue  the  computations  above  the  hydrostatic  limit  we 
adopt  a  method  of  trial  and  error  which  is  in  many  hydraulic 
problems  the  only  available  method.  We  assume  a  value  for 
the  swell  and  execute  the  computations  on  that  assumption. 
The  result  will  show  how  the  assumption  should  be  amended. 
Guided  by  preliminary  computations  which  need  not  be  intro- 
duced, I  adopt  0.732  as  the  rise  of  the  surface  at  middle  of  the 
seventh  mile.  This  makes  the  max.  depth  6. 732,  mean  depth 
4.488,  width  40.8  V6. 732  =  105.86,  cross-section  475.10,. 
velocity  =  2.5258.  We  here  take  c  —  79. 

Fall  in  the  seventh  mile  =  5280     \a         -  — -  =  1.2026. 

(79)    X  4-488 

This  result  makes  the  surface  at  the  middle  of  the 

seventh  mile  1.1269  +  0.6013  = 1.7282" 

above  what  we  may  call  the  pond-level.  Our 
assumption  would  make  it  0.732  -f-  i  foot  fall  in 
original  surface 1.7320 

At  the  end  of  the  seventh  mile  the  surface  of  the 

water  is  1.1269  +  1.2026  = 2.3295 

above  pond-level.     The  natural  surface  was....        2. 

Swell  of  stream  i  mile  above  the  hydrostatic  limit.  .        0.3295 

In  like  manner,  guided  by  preliminary  computations,  we 
assume  the  swell  at  the  middle  of  the  eighth  mile  o.  1 89,  max. 
depth 6. 1 89,  mean  4. 1 26,  width  101.50,  cross-section  =  4 1 8 . 79, 
velocity  =  2.8654.  Take  c  =  78. 


FLO  WAGE   OCCASIONED    BY  DAMS.  1 3 

(2  86C.A.Y 

Fall  in  eighth  mile  =  $2*°^*  x  4.126  =  l^269- 

This   result   makes  the  swell   at  the  middle  of  the      • 

eighth  mile  1.1269  +  1-202  +  0.8634  —  3  =.. .  .  0.1929 

Our  assumption  makes  it o.  1 890 

At  the  end  of  the  eighth  mile  the  swell  is 

1.1269  -f-  1.2026  -f  1.7269  —  4  =..... 0.0564 

That  is,  at  2  miles  above  the  hydrostatic  limit  the  swell  is 
about  two-thirds  of  an  inch. 

In  applying  these  methods  to  an  important  case,  the  en- 
gineer would  take  half-mile  and  quarter-mile  sections  near  the 
hydrostatic  limit  of  the  flowage.  He  would  draw  the  cross- 
sections,  compute  the  areas,  measure  the  wetted  perimeter,  and 
thence  compute  the  values  of  R.  He  would  also  be  guided  by 
the  nature  of  the  bed  and  banks  of  the  stream  in  rinding  the 
values  of  c. 

It  is  worth  while  to  remark  that  before  the  building  of  the 
dam  the  entire  power  of  the  stream  was  expended  in  giving 
motion  to  the  water.  After  the  water  is  raised  by  the  dam  a 
very  slight  fall  suffices  for  the  movement  of  the  water,  leaving 
the  greater  part  available  for  power. 

It  is  also  to  be  remembered  that  the  above  computation  of 
the  flowage  takes  account  only  of  the  immediate  and  usually 
temporary  effect  of  the  dam.  In  the  course  of  time  other 
agencies  come  into  operation  which  may  have  the  effect  of 
extending  the  flowage  much  farther  up  the  stream.  The 
stream,  in  high  water,  is  constantly  bringing  down  sediment, 
either  earthy  matters  held  in  suspension,  or  gravel  and  pebbles 
rolling  on  the  bottom.  The  heavier  matters  are  arrested  at  the 
head  of  the  pond  where  the  velocity  begins  to  slacken ;  the 
lighter  are  deposited  farther  down.  Both,  by  diminishing  the 
waterway,  tend  to  extend  the  swell  of  the  dam.  In  the  course 
of  years  these  deposits  consolidate  and  harden  and  do  not 
yield  readily  to  an  increased  velocity  of  the  current.  Some 
dams  are  carried  away  with  considerable  regularity  at  every 


14  NATURAL    WATERCOURSES. 

recurrence  of  extreme  high  water,  an  event  which  carries  with 
it  the  removal  of  the  accumulated  deposits.  In  this  case,  the 
evil  referred  to  only  becomes  apparent  upon  the  construction 
of  a  permanent  dam.  In  cases  of  litigation  between  millowners 
and  parties  claiming  to  be  aggrieved  by  flowage,  the  dam,  in 
order  to  demonstrate  that  it  does  not  create  the  flowage  com- 
plained of,  is  virtually  removed  by  opening  waste-gates  and 
drawing  down  the  pond  till  the  fall  is  practically  obliterated. 
It  is  urged  that  the  flowage  cannot  be  created  by  the  dam,  since 
it  does  not  disappear  upon  removal  of  the  same.  This  is  an 
inconclusive  test.  It  is  necessarily  made  at  a  low  stage  of  the 
stream  and  lasts  but  a  few  hours,  during  which  time  the  cur- 
rent is  entirely  inadequate  to  the  removal  of  the  deposits  which 
have  accumulated  in  the  course  of  years  at  the  head  of  the 
pond.  The  fact  remains  that  these  deposits  were  occasioned 
by  the  dam  and  would  disappear  upon  its  permanent  removal. 


CHAPTER    II. 
DAMS   FOR   WATER-POWER. 

IN  common  speech  a  dam  for  water-power  is  a  structure 
designed  to  create  a  head  or  fall  in  a  running  stream.  Strictly 
speaking,  the  fall  is  not  created  by  the  dam.  It  exists  in  the 
natural  condition  of  the  stream  distributed  over  a  greater  or 
less  portion  of  its  length.  The  effect  of  the  dam  is  to  concen- 
trate it  at  a  single  point  and  apply  the  power  previously 
expended  in  idly  chafing  the  channel,  to  the  turning  of  wheels 
and  giving  motion  to  machinery.  Another  class  of  dams  of 
distinctly  different  construction  have  important  relations  to 
water-power,  viz.,  storage-dams  designed  to  create  reservoirs 
for  holding  the  flow  of  abundant  periods  for  use  during  periods 
of  scarcity.  We  exclude  this  class  of  dams  from  present  con- 
sideration. 

Considerations  as  to  the  Form  of  Dams. — A  dam  may  fail 
in  several  ways : 

I.   It  may  be  overturned  or  shoved  aside  by  the  pressure 


typ^^-^x^^ 

FIG.  3. 

of  the  water,  for  which  reason  the  body  of  the  dam  must  have 
a  strength  and  solidity  sufficient  to  resist  the  utmost  pressure 
that  the  water  can  exert  against  it.  Often  the  stability  of  the 
dam  is  derived  from  the  weight  of  the  water  itself  (Fig.  3). 

15 


j6  DAMS  FOR    WATER-POWER. 

The  dam  is  inclined  so  that  the  pressure  acts  mainly  down- 
ward. A  wooden  dam  of  this  kind  sometimes  fails  by  floating. 
A  jam  of  ice,  drift,  or  logs  occurs  in  the  stream,  obliterating  the 
fall.  The  force  tending  to  hold  the  dam  down  then  wholly 
disappears  and  it  floats,  or  its  tendency  to  float  brings  it  into 
such  disarrangement  that  it  is  destroyed  when  the  jam  breaks. 
A  dam  under  such  conditions  should  never  depend  for  its 
stability  wholly  upon  the  pressure  of  the  water. 

2.  A   dam   may  leak  so    much    as   to   wholly  destroy  or 
seriously  impair  its  value.     For  this  reason,  every  dam  has  a 
part  specially  applied  with  reference  to  stopping  the  water. 
This  may  be   a  layer  of  planking,    of  stone    laid   in  cement 
mortar,  of  mortar  alone  applied  to  rough  stone,  or  of  a  bank 
of  earth.     Examples  have  recently  occurred  in  high  dams  of 
a  "skin  "  consisting  of  a  continuous  riveted  steel  plate. 

3.  The  water  may  find  its  way  under  the  dam,  and,  on  a 
soft  bottom,  destroy  it  by  washing  away  its  foundation.      For 
this  reason,  the  water-tight  portion  of  the  dam  must  go  deep 
enough  into  the  bottom  to  avoid  all  danger  of  undermining. 

4.  The  water   falling   over  a   dam,    in  the  case  of  a   soft 
bottom,  may  excavate  to  such  a  depth  as  to  engulf  the  dam  in 
the  cavity  or  so  weaken  its  hold  on  the  bottom  as  to  allow  it 
to  be  shoved  down-stream.     To  guard  against  this  action,  a 
dam,  in  such  a  situation,   must  have   an   apron   or   platform 
extending  some  distance  down-stream  to  receive  the  shock  and 
commotion  of  the  falling  water.      A  site  on  a  rock  bottom  may- 
be considered  as  provided  with  a  natural  apron  if  the  rock  is 
of  a  sufficiently  refractory  character. 

5.  In  a  friable  formation,  the  water  may  pass  around  the 
end  of  the  dam,  destroying  it  piecemeal,  or  destroying  its 
usefulness  by  creating  a  new  channel  for  itself.  This  danger 
is  met  by  abutments  at  each  end  of  the  dam,  rising  above  high 
water  and  connected  in  a  water-tight  manner  with  the  shores. 
On  rock  bottoms  the  abutments  are  often  furnished  by  nature. 
Very  often  the  mill  to  which  the  dam  pertains  forms  one  of 
the  abutments.  The  abutment  sometimes  rises  above  the 


CONSIDERATIONS  AS    TO    THE   FORM   OF  DAMS 


natural  level  of  the  bank  and  is  joined  to  the  high  ground  by 
an  earth  embankment  or  wall. 

A  dam  therefore  must,  in  general,  have  these  several  parts: 
(i)  a  body  called  the  overflow,  rollway,  or  spillway;  (2)  a 
water-tight  skin  or  diaphragm;  (3)  a  water-tight  connection 
with  the  bed  and  banks;  (4)  an  apron;  (5)  abutments. 

The  cross-section  of  the  dam  is  governed,  first,  by  the 
necessity  of  opposing  a  sufficient  resistance  to  the  pressure  of 
the  water.  This  is  determined  by  a  simple  computation  in 
which  the  principle  to  be  observed  is :  That  the  moment  of  the 
forces  tending  to  overturn  the  dam  must  be  less  than  the 
moment  of  the  forces  tending  to  resist  overturning.  Of  course 
these  rigorous  principles  of  statics  apply  but  imperfectly  to  this 
case,  and  the  results  are  of  but  limited  value.  The  method 
assumes  an  unyielding  foundation,  which  is  true  only  of  rock. 
It  ignores  the  strength  which  the  dam  derives  from  its  connec- 
tion with  abutments  natural  or  artificial,  and  it  assumes  the 
impossibility  of  one  layer  of  the  dam  yielding  with  reference  to 
another.  Still  it  is  an  aid  to  a  correct  comprehension  of  the 
problem. 

Let  Fig.  4  represent  a  dam  sustaining  the  pressure  of  water. 
Consider  one  foot  in  length  of  such  a  dam.  Let  H  represent 
the  height  of  the  .dam,  h  the 
greatest  height  of  water  to  be 
expected,  in  floods,  above  the 
top.  The  weight  of  a  cubic  foot 
•of  water  varies  somewhat  with 
the  temperature,  the  maximum 
t>eing  62.4  pounds.  For  conven- 
ience of  calculation  we  take  it  at 
1 6  cubic  feet  to  the  1000  pounds, 
being  62.  5  pounds  per  cubic  foot. 
The 'pressure  against  the  face  of 
the  dam  is 


62.5/7(^+4 


1 

—  *—  * 

\ 

1 

\  » 

1 

J 

\ 

\ 

c 

y///  fssrj  firm 

FIG.  4. 

1  8  DAMS  FOR    WATER-POWER. 

This  force  tends  to  overturn  the  dam  around  the  point  C.  It  is 
distributed  in  varying  intensity  over  the  face  of  the  dam.  Its 
effect  on  the  dam  is  the  same  as  that  of  an  equal  force  acting 
at  a  single  point,  called  the  centre  of  pressure.  When  the 
surface  of  the  water  is  at  the  top  of  the  dam,  the  centre  of 
pressure  is  at  one-third  the  height  above  the  bottom.  The 
moment  of  pressure  with  reference  to  C  is,  in  that  case, 

H* 
62.5-3-. 

In  the  general  case  under  consideration,  it  is  easier  to  find 
the  moment  directly,  without  reference  to  the  centre  of  pressure. 
This  moment,  as  explained  in  the  accompanying  note,*  is 


The  force  tending  to  resist  overturning  is  the  weight  of  I 
linear  foot  of  the  dam.  It  acts  through  the  centre  of  the  dam, 
at  a  distance  from  c  equal  to  one-half  the  breadth  b. 

It  is  often  convenient  to  designate  the  weight  per  cubic 
foot  of  the  masonry  and  the  water  by  symbols. 

*The  moment  of  a  force  with  reference  to  a  given  point  is  the  product 
of  the  force  (in  pounds)  by  the  perpendicular  distance  of  the  point  from  the 
line  of  action  of  the  force.  To  find  the  moment  of  pressure  on  the  vertical 
face  of  the  dam,  let  x  represent  heights  with  reference  to  the  point  C.  The 
moment  of  the  pressure  of  any  film  of  water  whose  height  is  dx  is- 
62  &c(ir-\-  h  -  x)dx  =  t>2.c,(Hxdx  -f  hxdx  -  x*dx\  The  total  moment  is 


Hxdx  +  hxdx  -  x*dx  =  62.5^-'  +  ^  - 


The  centre  of  pressure  is  the  point  where  the  same  moment  would  be 
produced  if  the  total  pressure  62.5  (¥-  +&*\  acted  there.  Let  X  =  the 
height  of  this  point  above  the  bottom,  then 

62.s(—  +HhX=  62. 
\2 


whence 


y_  _  HI  h 

--  =  (2a> 


CONSIDERATIONS  AS    TO    THE  FORM  OF  DAMS.         1  9 

Let  w  represent  the  weight  of  the  masonry  or  material  of 
the  dam  per  cubic  foot,  y  the  weight  of  the  water  per  cubic 

foot.  Then  s  =  —  =  the  specific  gravity  of  the  dam.  We 
have  wbH  Tor  the  weight  of  a  linear  foot  of  the  dam,  and  for 
its  moment  with  referenc 
the  condition  of  stability 


its  moment  with  reference  to  C,  wH  —  .     We  have  therefore  as 


or  otherwise  expressed, 


In  addition  to  the  tendency  of  the  pressure  to  overturn  the 
dam,  its  tendency  to  shove  the  dam  bodily  down-stream  must 
be  considered.  This  is  opposed  indirectly  by  the  weight  of  the 
dam  on  which  the  resistance  to  sliding  depends.  Smooth  stone 
slides  on  smooth  stone  under  a  horizontal  force  of  two-thirds  its 
weight.  To  cause  a  stone  to  slide  on  gravel  or  clay  requires 
a  force  nearly  equal  to  its  weight.  Generally  if  a  dam  is 
massive  enough  to  resist  overturning  it  will  resist  sliding.  In 
the  case  just  considered,  the  horizontal  pressure  on  the  dam  is 

(H         \ 
yH\  --  \-  h\.     The    weight  =  ivHb.      If  the   dam  rested  on 

smooth  rock,  it  would  be  liable  to  slide  if 


We   are    not    here   considering  the    diminution    of  weight    of 
masonry  by  immersion. 

A  rock  bottom  is  ordinarily  very  rough  and  irregular  by 
nature,  and  the  irregularities  may  be  artificially  increased,  so 
that  the  chance  of  sliding  is  very  remote.  On  a  soft  bottom, 
a  high  dam  has  been  known  to  move  down-stream,  not  by 
sliding,  but  by  a  yielding  of  the  formation  on  which  it  rests. 


20  DAMS  FOR    WATER-POWER. 

Effects  of  Flood  Height.— We  have  considered  the  increased 
pressure  on  the  vertical  face  of  a  dam  due  to  high  water.  High 
water  affects  the  forces  acting  on  a  dam  in  another  way.  The 
water  generally  rises  much  higher  on  the  down-stream  side 
than  above.  This  acts,  in  one  way,  in  favor  of  the  dam,  by 
'diminishing  the  pressure  tending  to  overturn  it.  It  acts,  in 
another  way,  against  the  dam  by  diminishing  the  effective 
weight.  Both  these  effects  are  easily  calculated. 

Where  water  goes  over  a  rollway  in  an  unbroken  sheet, 
and  is  in  contact  with  abutments  at  both  ends,  another  force 
comes  into  action  against  the  dam.      The  air  under  the  sheet 
is  rarefied,  the  atmospheric  pressure  against  the  down-stream 
face  of  the  dam  is  diminished,  while  it  acts  in  full  force  on  the 
up-stream  side.     No  accurate  experiments  have  been  made,  so 
far  as  I  am  aware,  to  determine  the  extent  to  which  this  action 
takes  place.     That  the  force  cannot  be  serious  will  appear  from 
the  following  consideration.     Its  tendency  is  to  diminish  the 
leap  of  the  falling  stream.      Its  greatest  possible  deleterious 
effect  would  be  to  press  the  stream  against  the  down-stream 
face  of  the  dam  (see  Fig.  4).      Any  action  in  excess  of  this 
would  be  in  favor  of  the  dam,   as  tending  to  resist  overturn. 
Its  maximum  effect  would  therefore  be  to  annul  the  horizontal 
component  of  the  water's  movement.      This  is  known  to  be 
the  velocity  due  to  one-third  of  the  depth  h.      It  appears  to 
me,  therefore,  that  this  effect  is  fully  allowed  for  by  adding  one- 
third  to  the  value  of  h  in  computing  the  force  acting  to  over- 
turn the  dam. 

Dams  of  rectangular  cross-section  have  thus  far  been  con- 
sidered, as  exhibiting  the  simpler  applications  of  the  principle 
of  moments.  Dams  of  masonry  are,  however,  more  commonly 
built  with  an  inclined  face,  there  being  some  economy  of 
material  in  this  arrangement.  The  inclination  of  the  up-stream 
face,  Fig.  5,  causes  the  resultant  pressure  to  pass  closer  to  the 
point  C,  thus  diminishing  the  lever-arm  of  the  moment  of 
pressure.  The  inclination  may  be  such  as  to  cause  the  resultant 
pressure  to  pass  through  C  or  even  below  it,  in  which  case  the 


EFFECTS   OF  FLOOD    HEIGH7\ 


21 


dam  has  stability  without  reference  to  the  weight.  Dams  are 
often  built  upon  this  principle,  as  the  one  indicated  at  Fig.  3, 
in  which  the  stability  of  the  dam  depends  wholly  on  the 
pressure  of  the  water. 

The   inclination   of  the   down-stream   face,   as   in   Fig.   6, 
lengthens  the  lever-arm  of  the  moment  of  resistance. 


FIG.  5.  FIG.  6. 

In  comparing  the  stability  of  different  forms  of  dam  we  do 
not  need  to  take  account  of  the  surcharge  h. 

For  the  case  of  a  triangular  dam  of  masonry  with  down- 
stream face  vertical,  the  water  standing  at  the  top  of  the  dam 
(Fig.  5),  the  resultant  pressure  is  perpendicular  to  AB  and 
goes  through  a  point  /,  such  that  Af  =  \fB.  If  we  make  the 
inclination  of  AB  such  that  the  resultant  goes  through  C,  we 


shall  have  BC  =  AC  1/2. 


AC" 

V2 


This  may  be  easily 


shown.  In  this  case  the  dam  has  an  excess  of  stability 
represented  by  the  moment  of  its  weight  with  reference  to  C. 
The  weight  acts  vertically  through  the  centre  of  gravity,  and  its 
line  of  direction  meets  the  base  at  a  distance  from  C  equal  to 
%AC.  For  greater  convenience  we  will  designate  the  sides  of 
the  triangle  by  the  small  letters  a,b,c, — a  being  opposite  the 
angle  At  b  opposite  £,  etc. 


22  DAMS  FOR    WATER-POWER. 

To  determine  the  dimensions  of  such  a  dam,  which  will 
barely  stand,  under  the  pressure  of  the  water,  we  proceed  as 

follows : 

Draw  Cn  perpendicular  to  AB,  and   Cd  perpendicular  t 

fd.  The  pressure  on  AB  is  y£ .  Its  moment  with  reference 
to  C  is  yc-Cd.  We  have  the  proportion  c  :  b  =  b  :  An, 
whence  An  =  *  and  Cd  =  Af  -  An  =  l-c  -  £  The  equa- 
tion of  moments  is 

f?(£  _  -\  =  wa-  b-  =  w—  (4) 

J2\3        cl  2-3  6 

Therefore  ^  -  ^  =  5^  or  ^  =  (j  +  ^)^2,  or,  replac- 
ing r8  by  its  value  az  -f-  ^2,  we  find,  since  a  =  H, 

u 

.....     (5) 


. 
The  cross-section  of  the  dam  is  —  -  = 


2^5+2 
For  a  rectangular  section  of  equal  stability  the  equation  of 

moments  is  wH  -  =  y-^>    whence  St>*  =  —   and    b  =  — =. 

H2 
The  cross-section  is  — = .     Therefore 


cross-section  of  triangular  dam         I       /     3^ 
cross-section  of  rectangular  dam       2  y  j  -j-  2* 

If  we  put  s  =  2.5,  we  find  the  cross-section  of  the  triangular 
dam  64. 5  per  cent  of  that  of  a  rectangular  dam  of  equal 
stability. 

For  a  dam  with  up-stream  face  vertical  and  down-stream 
face  inclined,  Fig.  6,  the  weight  acts  through  the  centre  of 


EFFECTS   OF  FLOOD   HEIGHT.  2$ 

•gravity    /,    at    a    horizontal    distance    from    C   equal    to    \b. 
Moment    of    water-pressure  =  y-^ .      Moment   of  resistance 

=   w  —  .  2~b  =  —HP,  whence  b  =  H\J ~      Cross-section 

JT  J  7g  / 

=  b —  =  — 4  /  -- ^..    For  a  rectangular  section  of  equal  stability 

rrs  r 

we  have  for  the  equation  of  moments/-^-  =  wHb—,  whence 


=H%; and  *= 

Cross-section  =  Hb  =  ff2\/—-~,  whence 

triangular  section          I       /$s       i       /3 
rectangular  section  ~~  2  y   2s  ~~  2  y   2  ~ 

or  the  triangular  section  is  61.2  per  cent  of  the  rectangular 
section. 

In  this  case  the  relation  of  the  cross-sections  appears  to  be 
independent  of  the  specific  gravity.  In  eq.  (6),  if  we  make 
the  specific  gravity  2.25,  the  ratio  is  0.631.  If  we  make  it  2, 
the  ratio  is  0.612,  the  same  as  in  (7).  It  appears,  therefore, 
to  be  practically  immaterial,  as  regards  stability,  which  side  of 
the  dam  is  inclined. 

The  mode  of  construction  of  a  dam,  and  its  connection  with 
the  bottom,  often  complicate  the  application  of  the  principle  of" 
moments.  The  preceding  discussion  assumes  that  the  up- 
stream face  of  the  dam  is  connected  with  the  bottom.  If  we 
could  suppose  the  dam  connected  with  the  bottom  at  C,  and 
the  bottom  accessible  between  B  and  C  to  the  water  of  the 
pond,  then  we  should  have  to  consider  the  pressure  acting 
upward  on  the  bottom  of  the  dam  as  one  of  the  forces  tending 
to  overturn  it,  and  should  find  it  necessary  to  greatly  increase 
the  weight  of  the  structure. 

The  preceding  results  show  an  economy  in  inclining  one 


24  DAMS  FOR    WATER-POWER. 

face  of  the  dam,  but  the  dimensions  arrived  at  are  not  such  as 
would  be  adopted  in  practice.  In  Figs.  5  and  6  the  resultant 
of  all  the  forces  acting  on  the  dam  goes  through  the  point  C. 
Practically  the  corner  would  crush  and  the  dam  would  falL 
Aside  from  this,  if  the  corner  holds,  the  dam  has  no  stability, 
being  as  likely  to  fall  as  stand.  Moreover,  a  sharp  crest  on 
the  top  of  a  dam  is  usually  inadmissible.  Considerations  apart 
from  stability  require  the  top  to  have  a  certain  breadth. 
Therefore,  to  the  outline  of  Fig.  5  or  6  a  rectangular  part 
should  be  added  to  give  the  required  stability. 

It  is  generally  admitted  among  engineers  that  the  resultant 
of  all  the  forces  acting  on  a  dam  should  pass  through  the 
middle  third  of  its  base.  This  gives  the  dam  a  wider  margin 
of  safety  than  is  usual  in  heavy  structures.  It  may  be  adopted 
in  the  case  of  a  dam  of  great  importance  whose  failure  would 
be  attended  with  disastrous  results.  It  is  also  convenient  to 
remember  in  the  frequent  case  where  hasty  and  approximate 
estimates  are  required.  In  a  case  like  that  of  Fig.  3  it  finds 
no  application.  The  rule  may  also  be  adopted  in  the  case  of 
bottom  which  cannot  be  regarded  as  entirely  unyielding.  The 
effect  of  the  horizontal  pressure  is  to  throw  the  weight  of  the 
dam  upon  one  side,  and  if  the  resultant  comes  too  close  to  the 
foot  of  the  down-stream  face,  the  ground  may  not  be  able  to 
sustain  the  weight.  Often  the  down-stream  face  is  curved, 
spreading  out  into  a  broad  toe  or  apron,  in  which  case  the 
literal  application  of  the  rule  would  lead  to  inadequate  dimen- 
sions. 

The  application  of  this  rule  to  a  dam  with  up-stream  face 
vertical,  down-stream  face  sloped,  is  indicated  at  Fig.  7.  The 
forces  are :  the  weight  acting  through  the  centre  of  gravity ; 
the  pressure  of  the  water  acting  horizontally.  /  is  the  centre 
of  gravity  of  the  triangle  ABC.  To  find  it,  bisect  the  base 
at  d.  Draw  Bd  and  lay  off  thereon,  from  d,  dl  equal  to  one- 
third  dB  The  centre  of  gravity  I'  of  the  rectangular  part 
ASe/is  at  the  centre  of  figure,— mid-height  and  mid-width. 
Draw  /'/  and  divide  it  at  /,  inversely  as  the  weights.  That  is : 


EFFECTS   OF  FLOOD    HEIGHT. 


if  the  weight  of  ABC  is  represented  by  7,  and  that  of  ABef 
by  12,  then  I'i  must  be  T7-ff  of/'/.  As  before,  let  h  represent 
the  depth  flowing  over  the  dam.  The  horizontal  pressure 


T 


I"         Tl 

, — -I 

FIG.  7. 


of  the  water  acts,  eq.  (20),  at  a  height  X  =  —\l 


above  the  bottom. 


When  //  =  o,  X  =  — . 


HI 
3V  +  ff:+2Aj 

We  can  draw  the 


two  lines  representing  the  forces  acting  on  the  dam.  From 
m,  their  intersection,  we  lay  off  the  vertical  ml  to  represent 
the  weight  of  the  dam,  and  the  horizontal  mo  to  represent  the 
pressure.  Complete  the  rectangle  mlno  and  draw  the  diagonal 
inn.  This  represents  the  resultant  of  the  forces  acting  on  the 
dam,  and  must,  according  to  the  above  rule,  fall  within  the 
middle  third  of  the  base.  If  this  condition  is  not  fulfilled,  we 
must  redraw  the  figure  with  a  different  value  of  Be  or  a 
different  inclination  of  BC. 

Fig.  8  represents  the  construction  when  the  up-stream  face 
is  inclined  and  the  down-stream  face  vertical.      In  this  case, 


26  DAMS  FOR    WATER-POWER. 

putting  c  to  represent  the  side  AB,  the  pressure  on  the  inclined 
face  is  ^(-  +  A     Moment  with  reference  to  A 

IH 


(8) 


*  is  the  common  centre  of  gravity,  m  the  intersection  of  the 
two  forces,  mo  represents  the  pressure,  ml  the  weight,  mlno  the 


FIG.  8. 

parallelogram  of  forces,  mn  the  resultant.  The  width  Be,  or 
the  inclination  of  AB,  must  be  Varied  till  mn  intersects  the 
base  at  the  right  point. 

Form  with  Reference  to  Discharge. — The  cross-section  is 
governed,  secondly,  by  the  consideration  of  passing  the  water 
in  a  manner  to  expose  the  dam  to  as  little  injury  or  chance  of 
injury  as  possible.  To  understand  the  conditions  of  this 
requirement,  we  must  examine  attentively  the  action  of  falling 


FORM    WITH  REFERENCE    TO   DISCHARGE.  2? 

water.  When  a  sheet  of  water  falls  over  the  perpendicular 
face  of  a  dam,  and  strikes  on  a  level  surface,  the  stream,  at 
certain  stages,  takes  the  form  shown  at  Fig.  9.  It  changes  its 


FIG.  9. 

direction  and  flows  with  unabated  velocity  along  the  bottom. 
At  a  the  stream  is  moving  horizontally  with  substantially  the 
velocity  due  the  fall.  At  b  the  stream  has  taken  its  normal 
depth,  that  is,  the  depth  determined  by  the  quantity  of  water 
and  declivity  of  the  bed,  and  moves  at  a  much  slower  velocity. 
The  transition  from  the  depth  a  to  the  depth  b  takes  place 
suddenly.  The  elevated  surface  of  the  water  moves  up-stream 
toward  c,  and  is  constantly  tumbling  over  into  the  swift  water. 
c  is  the  crest  of  a  wave,  which  does  not  move  like  waves  in 
deep  water,  but  remains  fixed,  and  is  constantly  breaking.  It 
is  called  a  standing  wave.  The  distance  of  c  from  the  falling 
stream  depends  upon  the  normal  depth.  As  this  increases,  c 
approaches  the  stream  and  in  a  high  stage  of  water  the  con- 
dition is  as  shown  at  Fig.  10.  The  water  closes  in  upon  the 


FIG.  10. 

falling  stream,  which  has  the  same  direction  as  before,  causing 
a  swift  current  for  some  distance  on  the  bottom.      On  the  sur- 


28  DAMS  FOR    WATER-POWER. 

face,  the  current  is  toward  the  falling  stream,  and  a  heavy- 
body,  as  a  log  or  block  of  ice,  is  carried  down  and  along  the 
bottom  with  great  velocity,  rises  to  the  surface  and  moves 
up-stream,  reaches  the  falling  stream  with  momentum  sufficient 
to  pass  through  it  and  strike  the  dam  with  great  violence.  It 
is  then  seized  by  the  current,  whirled  about,  striking  the 
bottom,  and  is  carried  down-stream.  It  sometimes  repeats  this 
cycle  of  movements  for  many  minutes,  till  it  chances  to  get 
beyond  the  range  of  the  whirling  motion. 

A  similar  eddy  or  vortex  occurs  between  the  stream  and 
the  face  of  the  dam.  This  is  the  more  extended  as  the  stage 
of  the  water  is  higher.  The  water  in  this  enclosed  space  may- 
rise  considerably  higher  than  the  general  level  below  the  dam, 
owing  to  the  exhaustion  of  the  air  as  already  alluded  to. 
These  commotions  destroy  the  velocity  and  momentum  of  the 
water,  as  brakes  destroy  the  momentum  of  a  train.  At  a. 
short  distance  below  the  dam,  the  water  pursues  its  course 
with  a  velocity  and  depth  determined  by  the  character  of  its 
bed. 

The  highest  flood,  one  whose  normal  depth  would  be  equal 
to  the  height  of  the  dam,  goes  over  the  latter  in  the  form 
indicated  at  Fig.  1 1 ,  and,  provided  the  abutments  hold,  it  is 


FIG.  it. 


doubtful  if  such  a  flood  is  as  trying  to  the  dam  as  one  of  more 
moderate  height.  A  heavy  body  riding  on  the  surface  would 
iot,  as  in  the  case  of  Fig.  10,  strike  the  dam,  but  the  eddy 
under  the  flood-sheet  takes  a  greater  development,  and  bodies 
drawn  into  it  are  liable  to  beat  against  the  dam. 


FORM    WITH  REFERENCE    TO  DISCHARGE.  2C> 

It  would  appear,  therefore,  that,  except  for  a  hard  rock 
bottom  and  a  very  solid  construction  of  the  dam,  a  perpen- 
dicular face  down-stream  is  to  be  avoided. 

The  down-stream  face  often  has  the  outline  of  Fig.   12, 


FIG.  12. 

leading  the  water  down  in  a  long  slope.  In  considering  such 
dispositions,  this  fact  must  never  be  lost  sight  of:  a  given 
amount  of  fall  imparts  the  same  velocity  to  water  whether  the 
latter  goes  down  an  incline  or  falls  freely.  The  friction  on  the 
incline  has  some  slight  effect  of  retardation,  but  not  enough  to 
affect  the  question.  Fig.  12  represents  the  situation  in  high 
water.  It  differs  from  the  case  of  a  perpendicular  face  only  in 
the  absence  of  the  eddy  next  the  dam.  In  this  case,  as  in  the 
others,  there  is  a  strong  current  toward  the  falling  stream,  and 
heavy  bodies  are  liable  to  stay  in  the  vicinity  of  the  dam, 
moving  up-stream  till  caught  by  the  water  coming  over  the 
dam,  then  plunging  under  water  and  battering  the  inclined 
face,  then  rising  to  the  surface  and  again  moving  up-stream. 
A  floating  body  goes  over  the  dam  in  a  different  manner  from 
an  equal  mass  of  water,  on  account  of  its  buoyancy.  Ice  has 
a  buoyancy  of  5  pounds  per  cubic  foot,  timber  often  as  much 
as  25.  A  log,  coming  over  such  a  dam,  plunges  into  the  swift 
current,  going  down-stream  near  the  bottom,  and  would  get 
clear  of  the  eddy  if  it  did  not  rise.  Its  buoyancy  causes  it  to 
rise  into  the  reverse  current,  which  arrests  its  motion  and 
carries  it  back  up-stream.  The  action  on  the  bottom  is  prob- 
ably somewhat  less  severe  in  this  case  than  in  the  case  of  a 
vertical  face.  The  stfeam  meets  with  more  resistance  before 
reaching  the  bottom,  which  diminishes  its  velocity.  On  a 


30  DAMS  FOR    WATER-POWER. 

smooth  artificially  prepared  bottom  this  consideration  has  force ; 
but  on  a  natural  bottom  with  obstructions  and  irregularities 
which  so  readily  change  the  direction  of  the  current,  the  latter 
must  be  supposed  to  act  with  equal  force  in  all  directions. 
The  direction  in  which  the  stream  approaches  the  bottom  is 
not  so  important  as  is  ordinarily  supposed.  On  a  bottom  of 
stratified  rock,  the  beds  horizontal  or  dipping  down-stream,  the 
action  of  an  inclined  stream  might  be  even  more  severe  than 
that  of  a  vertical  one.  The  main  advantage  secured  by  this 
construction  is  the  removal  of  the  destructive  action  to  a  greater 
distance  from  the  vital  parts  of  the  dam.  It  is  presumed,  of 
course,  that  this  construction  would  not  be  adopted  except  for 
a  rock  bottom.  Many  formations,  however,  which  are  classed 
as  rock  are  susceptible  of  rapid  wear.  On  such  a  bottom  the 
effect  of  the  form  of  Fig.  12  would  be  to  scour  out  a  hollow 
place  at  the  foot  of  the  slope.  This  extends  and  gives  full 
development  to  the  reverse  eddy,  which  has  the  effect  of 
extending  the  excavation  under  the  slope.  If  the  foot  of  the 
slope  rests  upon  the  bottom,  it  is  rapidly  destroyed.  If  it  is  so 
constructed  that  a  considerable  length  of  it  will  stand  without 
support,  the  excavation  extends,  more  slowly  but  still  surely, 
till  the  safety  of  the  whole  structure  is  brought  in  question. 
The  sloping  part  may  have  the  effect  to  greatly  defer  this  result, 
but  cannot  prevent  it. 

Dams  with  Steps.— An  advantage  is  sometimes  thought 
to  be  gained  by  dividing  the  fall  into  a  number  of  small  falls 


FIG.  13. 


or  steps  separated  by  level  "treads,"  as  in  Fig  13  The 
water  is  assumed  to  lose  at  each  step  the  velocity  acquired  in 
falling,  and  to  reach  the  bottom  with  only  the  velocity  due  to 


DAMS    WITH  STEPS.  31 

the  last  step.  This  would  be  a  correct  assumption  if  the  steps 
were  far  enough  apart.  To  judge  whether  this  result  is  obtain- 
able within  any  reasonable  constructive  limits,  it  is  necessary 
to  form  some  idea  of  the  mode  in  which  the  water  traverses 
such  a  dam. 

We  have  seen  that  water  falling  over  a  dam  and  striking 
on  the  bed  of  the  channel,  supposed  to  be  smooth,  glides  away 
from  the  foot  of  the  dam  in  a  thin  sheet  with  a  velocity  very 
near  that  due  the  fall.  The  depth  «,  Fig.  9,  for  a  fall  of 
4  feet  would  not  in  ordinary  stages  be  more  than  one-fourth  or 
one-fifth  that  in  the  general  bed  of  the  stream,  which  we  have 
termed  the  normal  depth.  This  normal  depth  tends  to  estab- 
lish itself  in  all  parts  of  the  channel  below  the  dam.  It  results 
from  this  tendency  that  a  mass  of  water  is  constantly  rolling 
back  upon  the  escaping  stream  and  being  drawn  away  with  it, 
an  action  tending  to  the  rapid  extinction  of  velocity.  The 
distance  below  the  dam  at  which  the  velocity  becomes  uniform 
and  normal  is  marked  by  the  point  where  the  water  ceases  to 
flow  up-stream.  This  distance  is  much  less  on  a  rough  bottom 
than  on  a  smooth  bottom.  The  movement  is  often  greatly 
modified  by  a  condition  which  commonly  exists  at  the  foot  of 
a  dam,  viz. ,  a  deep  pit  or  basin  excavated  by  the  water.  On 
a  smooth,  level,  planked  bottom  it  is  not  probable  that  this 
distance  would  be  less  than  five  times  the  fall.  We  can  readily 
see  that  if,  at  the  point  b,  Fig.  9,  the  water  took  a  second 
drop,  the  tendency  to  the  extinction  of  velocity  would  be 
greatly  diminished.  The  tendency  to  the  establishment  of  a 
normal  depth  would  be  counteracted  by  the  second  fall. 
There  would  be  no  mass  of  water  flowing  up-stream,  and  the 
water  would  shoot  over  the  second  step  with  but  little  abate- 
ment of  the  velocity  acquired  by  going  over  the  first.  Briefly 
stated,  the  water,  in  going  over  such  a  dam,  can  undergo  no 
commotion  tending  to  destroy  its  velocity,  and  therefore  its 
velocity  is  not  destroyed.  Of  course,  if  the  second  step  were 
removed  to  a  very  great  distance  from  the  first,  a  normal  depth 
corresponding  to  the  nature  of  the  channel  and  volume  of  water 


32  DAMS  FOR    WATER-POWER. 

would  establish  itself.  The  preceding  considerations,  however, 
show  how  exceedingly  unfavorable  the  conditions  are  to  the 
extinction  of  velocity.  These  conditions  become  more  unfavor- 
able as  the  depth  increases,  till  in  high  flood  the  water  goes 
over  the  dam  almost  precisely  as  over  a  straight  incline.  In 
any  stage  above  the  lowest,  it  is  evident  that  the  steps  can 
have  little  effect  in  moderating  the  velocity,  without  giving  the 
dam  a  profile  greatly  in  excess  of  that  called  for  by  considera- 
tions of  stability.  Should  such  a  dam  be  built  under  the 
impression  that  water  going  over  it  would  reach  the  bottom 
with  a  low  velocity,  dispositions  necessary  to  secure  the  bottom 
from  abrasion  would  be  likely  to  be  neglected,  to  the  increase 
of  the  risk  of  disaster.  This  form  of  dam  would  be  improved 
by  giving  the  tread  between  two  consecutive  steps  an  inclina- 
tion up-stream,  forming  a  basin  for  stilling  the  commotion  and 
moderating  the  shock  of  floating  bodies.  It  is  to  be  doubted, 
however,  whether  any  form  of  dam  has  less  to  recommend  it 
for  adoption  than  this.  It  will  appear  later  that  no  form  of 
dam  suffers  more  severely  than  this  from  ice  and  logs. 

Inclination  of  Top  of  Dam.— It  is  usual  to  give  the  top  of 
the  dam  an  inclination,  rising  toward  the  down-stream  side,  to 
facilitate  the  passage  of  ice  and  floating  bodies,  the  portion  ab, 
Fig.  14,  rising  from  12  to  30  inches,  according  to  the  size  of 


FIG.  14. 

the  bodies  to  be  looked  for.  Blocks  of  ice  on  northern  rivers 
may  float  to  a  depth  of  40  inches,  but  such  blocks  would  not 
move  at  all  unless  there  was  some  depth  of  water  going  over 
the  dam.  Ice  is  liable  to  move  in  masses  which  make  it 


DAMS   CURVED    IN  CROSS-SECTION.  33 

formidable  even  at  low  velocities.  This  arrangement  is  to  be 
recommended  for  a  low  dam,  but  the  necessity  for  it  diminishes 
as  the  height  of  the  dam  increases.  It  is  manifest  that  in  the 
case  of  a  high  dam,  in  any  stage  of  water  such  that  floating 
bodies  could  strike  the  dam,  they  must  approach  it  with  a 
very  low  velocity. 

Dams  of  rectangular  outline  have  sometimes  been  built 
with  a  sloping  bank  of  earth  or  loose  stone  on  the  up-stream 
side.  Whatever  advantage  may  be  expected  from  this  arrange- 
ment, it  certainly  has  one  serious  objection.  It  shoals  the 
waterway  approaching  the  dam,  and  increases  the  velocity  with 
which  floating  bodies  strike  it.  At  a  dam  on  a  rapid  stream, 
such  a  bank  may  be  expected  to  form  naturally  in  the  course 
of  time,  and  the  crest  should  be  shaped  with  reference  to  that 
contingency. 

Dams  Curved  in  Cross-section. — The  execution  of  curved 
outlines  in  timber-work  presents  no  insuperable  difficulty,  as  is 
well  understood  in  ship-building,  but  they  involve  methods  not 
familiar  to  millwrights  and  are  seldom  attempted  in  dam  con- 
struction. Masonry  is  not  subject  to  this  limitation,  and  of  late 
many  masonry  dams  have  been  built  with  curved  faces,  whereby 
it  is  thought  that  some  advantage  is  gained. 

The  typical  outline  of  such  a  dam  is  the  line  mabd,  Fig. 
15,  viz.,  the  curve  ma,  the  inclined  straight  line  ab,  and  the 
curve  bd.  In  some  cases  the  line  ab  is  wanting,  and  a  and  b 
coincide,  forming  a  reversed  curve.  The  summit  m  is  some- 
times joined  to  the  up-stream  face  by  a  horizontal  line  mi, 
sometimes  by  an  inclined  line.  Down-stream  from  d  the  dam 
is  constructed  according  to  the  nature  of  the  ground.  For 
rock  of  moderate  hardness  the  surface  would  continue  level  for 
some  little  distance  and  terminate  in  a  vertical  face.  This 
vertical  face  is  usually  rendered  necessary  by  the  irregular 
shape  of  the  bed.  If  the  bed  were  level  and  smooth,  the 
down-stream  face  could  join  it  by  a  curve  having  its  tangent- 
point  at  d,  but  this  is  usually  impossible.  Sometimes  the  toe 
is  so  formed  as  to  give  an  upward  direction  to  the  water,  as  at 


34  DAMS  FOR    WATER-POWER. 

Fig.  15*.  in  the  expectation  that  the  abrasive  action  is  thereby 
carried  farther  from  the  dam.  It  may  be  doubted  if  any  real 
advantage  results  from  this  arrangement.  It  gives  a  wider 
leap  to  the  stream  and  tends  to  diminish  the  velocity  with 
which  it  strikes  the  bottom.  It  gives  greater  opportunity 
for  the  development  of  horizontal  eddies  under  the  stream,  and 
exposes  the  toe  in  greater  measure  to  the  impact  of  floating 


FIG.  15.  FIG.  i5«. 

bodies  carried  by  the  reverse  current.  In  high  water,  when 
the  down-stream  surface  comes  well  up  on  the  curved  face  of 
the  dam,  such  refinements  of  construction  cut  no  figure,  unless 
it  be  the  following:  Logs  and  blocks  of  ice,  in  passing  the 
curved  surface  of  the  dam,  are  subject  to  a  centrifugal  force 
which  causes  them  to  hug  the  surface.  This  action  is  not 
necessarily  injurious  between  b  and  d,  where  there  is  no  danger 
of  dislodging  a  stone.  It  is  liable  to  act  injuriously  upon  the 
exterior  stones  of  the  toe.  Suppose  a  3<D-foot  dam  and 
assume  a  radius  of  20  feet  in  the  curve  of  the  toe.  A  heavy 
body  would  reach  this  curve  with  a  velocity  of  something  like 
44  feet  per  second  and  would  exert  thereon,  while  passing,  a 

W      44  X  44 
pressure  of—  X  =  Wx  3,   i.e.,  a  pressure  of  three 


DAMS   CURVED   IN   CROSS-SECTION.  35 

times  its  normal  weight.  The  frictional  pull  resulting  from 
this  pressure  must  have  a  strong  tendency  to  dislodge  the 
stones  of  the  toe. 

The  top  or  upper  part  of  the  face,  commencing  at  m,  is 
sometimes  formed  to  the  curve  which  the  overflowing  stream 
would  take  if  the  down-stream  face  were  perpendicular.  This 
curve  varies  with  the  quantity  of  water  passing  the  dam,  but  if 
it  is  correct  for  the  highest  stage  of  the  water,  the  water  will 
follow  it  at  all  other  stages.  The  form  of  this  curve  is  deter- 
mined as  follows  : 

Let  v  =  the  horizontal  velocity  of  the  stream  at  m.  Then, 
at  any  short  time  t  after  the  particle  of  water  under  considera- 
tion has  passed  /«,  it  will  have  moved  horizontally  a  distance 
*vt  and  fallen  vertically  a  distance  ^/2,  where  g  represents  the 
velocity  acquired  by  a  heavy  body  in  falling  one  second.  It 
is  well  known  that  the  curve  is  a  parabola  whose  equation  is 

<r/2 

of  the  form  j/2  =  zPx,  in  which  y  =  vt,  and  x  =  —  .      There- 

to1 

fore  v*tz  =  Pg-t'*,  and  P  =  —  ,  from  which  we  have  the  equation 

of  the  curve 


(9) 


From  an  investigation  published  by  the  writer  in  the 
Engineering  News  of  September  29,  1892,  it  appears  that  v  is 
the  velocity  due  to  one-third  the  "depth  on  the  dam,"  this 
•expression  being  understood  to  mean  the  height  of  pond-level 
above  the  crest  of  the  dam. 

It  is  manifest  that  the  form  of  the  top  might  deviate 
materially  from  that  of  Fig.  15.  It  might  have  the  outline 
lima  without  affecting  the  movement  of  the  water  injuriously. 
It  might  have  the  outline  I  i  ink  a  with  no  more  serious  disad- 
vantage than  a  tendency  in  the  stream  to  leap  clear  of  the  dam 
and  strike  it  again  at  a  lower  point,  a  matter  of  no  importance. 
It  must  be  borne  in  mind  that  where  the  overflowing  stream  is 
confined  between  abutments,  the  action  of  the  atmosphere 


36  DAMS  FOR    WATER-POWER. 

tends  strongly  to  hold  the  stream  to  the  down-stream  face  of 
the  dam. 

The  form  of  the  dam  at  the  bottom  is  much  more  important 
than  that  at  the  top.  Water  falling  over  a  dam  reaches  the 
lower  level  with  the  velocity  due  to  the  fall.  At  a  distance 
down-stream  which  may  not  exceed  four  or  five  times  the 
height  of  the  dam,  we  find  the  water  flowing  with  a  uniform 
current  and  moderate  velocity.  At  the  former  point  the  actual 
energy  of  the  water,  due  to  its  mass  and  velocity,  may  be 
50  ooo  horse-power ;  at  the  latter  not  more  than  two  or  three 
hundred.  What  has  become  of  this  enormous  amount  of 
energy  ?  As  a  train  of  cars  is  brought  to  rest  by  the  friction 
of  the  brakes,  this  mass  of  swift-moving  water  is  brought  to 
rest  by  the  friction  of  its  individual  particles  upon  each  other 
and  upon  the  bed.  The  latter  kind  of  friction  tends  to  abrasion 
and  injury;  the  former  is  harmless.  In  the  case  of  the  train 
as  well  as  that  of  the  water,  -the  energy  is  transformed  into 
heat.  In  the  former,  the  energy  being  consumed  by  the  brakes, 
these  parts  are  heated  to  a  very  high  temperature.  In  the  case 
of  the  water,  when  each  particle  takes  part  in  the  expenditure 
of  energy,  the  resultant  heat, is  distributed  through  the  entire 
mass  and  does  not,  in  the  ordinary  case,  raise  the  temperature 
enough  to  be  detected  by  the  most  delicate  thermometer.  To 
raise  the  temperature  of  the  water  by  one  degree  Fahrenheit 
would  require  a  fall  of  772  feet.  There  is  another  point  of 
difference  not  to  be  lost  sight  of  between  the  two  cases,  viz. : 
in  the  moving  train  the  energy  consumed  by  friction  is  propor- 
tional to  the  velocity ;  in  the  other  case,  to  the  square  of  the 
velocity.  Energy,  therefore,  is  destroyed  much  more  rapidly 
in  the  latter  case  than  in  the  former. 

The  toe  of  the  dam  should  be  formed  with  reference  to  the 
extinction  of  velocity  without  injury  to  the  structure.  On  a 
bottom  liable  to  abrasion  the  ideal  form  would  be  that  of 
Fig.  16,  in  which  the  water  falls  into  a  basin  of  considerable 
extent,  with  smooth  and  rounded  outlines,  exhausts  its  energy 
in  whirlings,  tumblings,  and  commotions,  and  resumes  its 


OUTLINE   OF  DAM  IN  PLAN. 


37 


course  in  the  natural  bed  of  the  stream  divested  of  all  power 
for  mischief.  Kven  in  this  arrangement  the  parts  at  the 
entrance  to  the  basin  are  liable  to  heavy  blows  from  floating 


FIG.  1 6. 

bodies  carried  up-stream  by  the  reverse  current,   and  should 
have  the  solidity  to  withstand  such  blows. 

Outline  of  Dam  in  Plan.— Old  dams  are  often  met  with  in 
the  form  indicated  by  Fig.  17,  a  and  b,  obtaining  a  great  length 
by  running  obliquely  across  the  stream,  as  at  a,  or  consisting 


FIG.  17. 

of  two  branches  converging  to  a  point,  as  at  b.  The  only 
rational  purpose  that  can  be  discovered  in  this  arrangement  is 
the  diminution  of  the  swell  in  time  of  flood.  By  giving  the 
dam  a  greater  length  of  overflow  it  prevents  the  water  from 
rising  as  high  as  it  otherwise  would.  In  every  other  point  of 
view  the  arrangement  is  bad.  It  is  especially  bad  in  its  effects 
upon  the  banks  and  bed  below  the  dam.  In  the  arrangement 
a  the  current  is  thrown  with  great  force  upon  the  bank  at  the 
upper  end,  and  it  forms  an  eddy  and  reverse  current  at  the 
lower  end.  In  b  the  water  concentrates  in  the  middle  of  the 
stream,  causing  a  very  swift  current  there,  which  continues  a 


210939 


38  DAMS  FOR    WATER-POWER. 

long  distance  down-stream,  causing  eddies  and  reverse  currents 
on  both  sides.  On  a  soft  bottom  these  effects  are  very  objec- 
tionable, as  greatly  increasing  the  extent  and  cost  of  works  for 
protection  of  the  bed  and  banks.  On  a  formation  of  solid  rock 
these  objections  have  no  force.  In  moderate  stages  of  the 
river  these  arrangements  allow  the  water  to  pass  with 
diminished  depth  upon  the  dam,  and  so  diminish  the  head 
available  for  power.  In  the  highest  stages  it  is  doubtful  if  they 
cause  any  material  diminution  of  the  swell. 

Dams  Curved  in  Plan,  and  intended  to  resist  pressure  of 
water  upon  the  principle  of  the  arch,  are  often  built.  From 
analogy  with  stone  bridges  and  other  arched  structures,  this 
form  is  thought  to  give  some  advantages  over  a  straight  dam 
in  point  of  stability.  This  claim  may  be  answered  as  follows : 
All  material  resists  pressure  or  strain  by  undergoing  a  certain 
deformation.  A  beam  sustains  a  load  by  bending.  It  is  only 
in  virtue  of  this  deformation — extension  of  the  fibres  on  one 
side  and  compression  on  the  other — that  the  power  of  the  beam 
to  sustain  a  load  is  called  into  action.  An  arch  resting  on  its 
centring  has  no  strain  to  resist.  On  removal  of  the  centring, 
the  arch  settles  a  little,  and  all  its  members  undergo  a  slight 
change  of  form  and  volume.  It  is  in  virtue  of  this  change  that 
the  arch  acquires  the  power  to  resist  the  strain  to  which  it  is 
exposed. 

An  arched  dam  is  in  a  radically  different  condition  as  to 
strain.  Its  necessarily  close  connection  with  the  bed  of  the 
stream  does  not  permit  the  lower  part  to  act  as  an  arch  with- 
out breaking  its  connection  with  the  bed,  which  would  be 
attended  with  inconvenience  and  danger. 

For  a  dam  exceeding  500  feet  in  length,  even  assuming  it 
to  act  as  an  arch,  the  dimensions  required  to  resist  the  arch 
strain,  and  the  workmanship  and  materials  required  to  fit  it  for 
that  strain,  would  make  the  dam  more  expensive  than  if  built 
straight  and  proportioned  to  meet  the  strain  acting  on  a 
straight  dam. 

The   fact   nevertheless    remains    that   curved    dams    have 


DAMS    CUKVED    IN  PLAN.  39 

been  built,  and  have  stood  successfully,  with  dimensions  much 
lighter  than  would  have  been  thought  necessary  for  straight 
dams.  These  are  mostly  dams  of  great  height,  built  to  close 
narrow  ravines  and  form  reservoirs  for  purposes  of  irrigation. 
The  Bear  Valley  Dam  *  in  San  Bernardino  County,  California, 
is  64  feet  high  and  is  curved  to  a  radius  of  335  feet.  The 
lower  16  feet  of  it  has  a  thickness  of  22  feet.  The  upper  48 
has  a  thickness  of  8|  feet  at  bottom  and  2£  at  top. 

These  dams  are  not  liable  to  overflow.  The  drainage-area 
commanded  by  them  is  not  of  great  extent,  and  the  water 
seldom  rises  to  the  summit  of  the  dam.  When  it  approaches 
that  level,  sluices  are  opened.  These  conditions — a  narrow 
gorge  bounded  by  nearly  perpendicular  walls  of  rock,  a  limited 
drainage-area  and  consequent  absence  of  overflow — seem  to 
give  some  application  for  curved  dams.  For  ordinary  overflow 
dams  of  moderate  height  and  considerable  length  there  appears 
to  be  no  advantage  in  a  curved  horizontal  outline. 

As  to  its  effect  upon  the  bed  and  banks  of  the  stream  this 
form  has  no  advantage.  The  escaping  water  concentrates  in 
the  middle  of  the  stream,  forming  a  very  swift  current  there, 
accompanied  by  eddies  and  reverse  currents  on  each  shore. 
In  a  formation  liable  to  abrasion,  any  arrangement  of  the  dam 
which  concentrates  the  current  in  one  part  of  the  stream  is 
bad,  as  the  swift  water  extends  further  down  the  stream  than 
it  would  if  the  water  left  the  dam  with  a  uniform  velocity. 

A  straight  dam  running  square  across  the  stream  has  a 
great  advantage  in  this  respect.  The  water  leaves  it  with 
uniform  velocity,  encounters  uniform  retardation,  and  all  comes 
to  the  normal  depth  at  the  same  distance  below  the  dam. 
Where  liability  to  undermining  is  an  important  consideration, 
this  outline  should,  with  very  rare  exceptions,  be  adopted.  On 
a  hard  rock  bottom,  with  rock  banks,  such  considerations  are 
of  no  force,  and  in  such  situations  the  formation  and  contour 
often  dictate  a  curved  or  broken  outline  for  the  dam. 

*  Eighteenth  Annual  Report  U.  S.  Geol.  Survey,  Part  IV,  p.  683. 


CHAPTER   III. 
CONSTRUCTION   OF  DAMS. 

HAVING  set  forth  some  of  the  general  principles  governing 
the  form  of  dams,  we  may  now  proceed  to  consider  some  prac- 
tical examples  of  their  construction,  commencing  with  the 
simplest  case.  Figs.  18,  19,  and  20  represent  a  dam  built  by 


FIG.  18. 


FIG.  19. 

the  author  in  1885  across  the  Sangus  River  in  Massachusetts 
for  the  purpose  of  measuring  the  flow  of  the  stream.  The  head 
created  by  the  dam  did  not  need  to  be  more  than  3  feet,  and 
it  was  not  necessary  to  continue  the  measurement  more  than  a 

40 


MEASURING    THE   FLOW  OF   THE  STREAM. 


t::.r 


42  CONSTRUCTION  OF  DAMS. 

year,  so  that  a  substantial  structure  was  not  required.      The 
bed  of  the  stream  was  gravel  to  an  indefinite  depth.      At  the 
proposed  location  of  the  dam  the  bed  was  levelled  for  a  space 
12  feet   up  and    down   stream,    24  feet   transverse, 
space  were  imbedded  across  the  stream  three  8  X  8-inch  sills, 
each  confined  by  three  i-inch  iron  rods  driven  through  holes 
in  the  sill  and  12  feet  deep  in  the  ground,  the  process  of  driv- 
ing forming  a  head  on  the  rod  which  held  the  timbers  securely. 
On  these  timbers  was  laid  a  flooring  of  2-inch  plank  securely 
spiked  down,  forming  an  apron  over  which  the  water  flowed  2 
or  3  inches  deep  until   everything  was   ready  for   raising  it. 
Along  the  up-stream  timber,  a  row  of  spiling,*  consisting  of 
2-inch  tongued  and  grooved  plank,  was  driven  to  a  depth  of 
2  or  3  feet,  and  continued  on  each  side  to  meet  the  embank- 
ment which  formed  the  remainder  of  the  dam.      Along  the  sill 
this  spiling  was  cut  off  2  or  3  inches  below  the  top  of  the  sill, 
and  spiked  thereto,  leaving  a  footing  on  the  sill  for  the  closing 
plank.     Near  the  ends  of  the  up-stream  sill   two  upright  posts 
a  and  b  were  inserted,   confined  by  mortise   and   tenon,   and 
connected  by  a  light  beam  ab.     Two  similar  beams  were  also 
inserted  with  their  outer  ends  resting  on  the  natural  bank,  and 
to  these  were  spiked  the  spiling  outside  the  weir,  both  the  spil- 
ing and  timber  being  partly  imbedded   in   the   embankment. 
The  arrangements  required  to  fit  the  dam  for  water-measuring, 
which  need  not  be  here  described,  were  then  added,  and  the 
posts  were  braced  from  the  down-stream  side  as  indicated  at  c 
and  d.      All  this  work  was  done  without  requiring  the  work- 
men to  stand  in  water  over  their  shoes.      Then  the  short  planks 
connecting  the  beam  ab  with  the  up-stream  sill  were  inserted, 
narrowing  the  opening  until  the  rush  of  water  became  formid- 
able.     Then  the  remaining  plank  were  joined  together  in  the 
form  of  a  gate,  and  dropped  into  place,  whereupon  the  water 
rose  and  flowed  over  the  weir.     The  planking  being  dry  soon 
swelled  so  as  to  stop  all  leakage. 

This,  although  but  little  above  the  toy  size,  contained  all 

*  The  term  Spiling  is  applied  to  sheet-piling  driven  by  hand. 


DAMS   OF  TIMBER  AND  EARTH.  43 

the  elements  of  the  largest  dam,  and  could,  no  doubt,  be 
applied  on  a  larger  scale.  On  the  I  3th  of  February,  1886,  a 
flood  in  the  stream  went  over  the  dam  so  deep  that  its  position 
was  only  indicated  by  a  ripple.  On  the  subsidence  of  the 
water,  both  dam  and  embankment  were  found  entirely  un- 
injured, the  latter  owing  its  safety  to  the  fact  of  its  being 
solidly  frozen. 

Figs.  21  and  22  show  a  dam  of  timber  and  earth,  suited 
to  a  formation  of  sand,  gravel,  or  clay,  with  no  rock  or  heavy 
boulders.  It  is  represented  as  raising  a  head  of  8  feet,  and 
might  no  doubt  be  applied  up  to  a  head  of  12.  There  is  no 
rational  purpose  to  be  gained  by  giving  such  a  dam  a  curved 
outline  in  plan,  neither  do  the  situations  to  which  it  is  appli- 
cable ever  call  for  a  change  of  direction  by  an  angle,  which 
would  introduce  serious  constructive  difficulties.  It  usually 
runs  straight  across  the  stream,  at  a  right  angle  to  the  general 
direction  of  the  latter,  as  near  as  may  be.  In  profile,  all  that 
is  attempted  in  the  way  of  moderating  the  action  of  the  water 
upon  the  apron  is  to  lead  the  water  from  the  dam  in  a  slope. 

The  crest  of  the  spillway  consists  of  a  heavy  timber  sup- 
ported on  round  piles  and  joined  to  a  line  of  sheet-piling. 
The  sills  for  sustaining  the  planking  also  rest  upon  round  piles. 
A  row  of  sheet-piling  runs  along  the  up-stream  and  down- 
stream faces  of  the  spillway  and  extends  beyond  the  same  as 
far  as  is  necessary  to  sustain  the  bank  which  joins  the  spillway 
to  the  high  ground  on  each  side  of  the  stream.  Reliance  for 
water-tightness  is  placed  mainly  upon  the  central  line  of  sheet- 
piling.  The  upper  row  is  chiefly  useful  in  the  process  of  con- 
struction, otherwise  it  might  be  dispensed  with.  In  any  case 
it  need  not  be  sheet-piling  properly  so  called,  but  spiling  driven 
by  hand.  For  a  dam  not  exceeding  8  feet  in  height  it  is 
probable  that  all  the  sheet-piling  shown  might  be  of  thai 
character.  The  lower  row  is  necessary  to  protect  the  interior 
of  the  spillway  against  the  wash  of  the  overflow,  as  well  as  to 
exclude  the  water  of  the  lower  level  during  construction 
Fig.  21  shows  the  sheet-piling  spiked  to  the  sill.  This  is  more 


44 


CONSTRUCTION  OF  DAMS. 


DAMS   OF  TIMBER  AND   EARTH. 


45 


46  CONSTRUCTION  OF  DAMS. 

in  accordance  with  modern  methods,  which  avoid  carpenter- 
work  by  the  use  of  iron  wherever  possible.  In  old  dams  the 
methods  indicated  at  a  and  b  are  more  common.  A  continuous 
groove  is  cut  in  the  sill  to  receive  a  continuous  tenon  cut  on 
the  heads  of  the  sheeting-plank.  This  tenon  is  covered  with 
a  strip  of  canvas  soaked  in  hot  tar  before  putting  the  sill  in 
place.  The  crest-sill  should  be  18  inches  square,  giving 
4  inches  each  for  the  rabbet  in  which  the  planking  rests,  and 
10  inches  face  showing  above  the  planking.  The  other  sills 
may  be  12  X  12.  The  side  walls  of  the  spillway  are  of  plank- 
ing bolted  to  special  piles,  which  are  indicated  as  round  piles 
flatted  to  receive  the  planking  after  they  are  driven.  They  are 
planked  on  both  sides,  and  are  fitted  with  a  cap  which  is  not 
shown.  These  piles  are  sometimes  dispensed  with  and  are 
replaced  by  uprights  mortised  into  the  sills  at  the  bottom  and 
into  a  cap  at  the  top,  which  latter  is  sustained  by  iron  rods 
running  into  the  bank  and  fastened  by  earth  anchors,  a  con- 
struction which  facilitates  repairs.  The  line  of  sheet-piling 
connected  with  the  crest-sill,  after  passing  the  side  walls  of  the 
spillway,  reaches  to  the  surface  of  the  ground  and  extends  into 
the  bank  as  far  as  need  be.  This  part  of  the  work  if  left  in 
contact  with  vegetable  mould  is  peculiarly  liable  to  decay; 
much  more  so  than  if  in  contact  with  clay  or  sand.  On  this 
account  a  construction  is  sometimes  adopted  which  does  not 
require  the  piling  to  reach  the  surface.  The  piling  is  cut  oft 
at  the  level  of  the  crest  of  the  spillway,  where  it  may  be 
assumed  to  be  always  wet,  and,  flush  with  the  top,  wale-pieces 
are  bolted  on  to  form  a  bed  12  inches  wide.  On  this  bed  a 
wall  of  brick  one  or  one  and  a  half  bricks  thick  is  laid  in 
hydraulic  mortar  reaching  to  the  surface.  Such  a  wall  has, 
it  is  true,  but  slight  stability,  but  it  will  stand  well  if  the  earth 
embankment  remains  intact.  The  sheet-piling  which  sustains 
the  bank  above  and  below  is  provided  with  wale-pieces,  which 
are  united  by  long  tie-rods  reaching  through  the  bank  and 
furnished  with  gaskets  to  prevent  the  water  from  following 
them. 


DAMS   OF   TIMBER  AND  EARTH.  47 

The  space  under  the  spillway  is  packed  with  clay  or  bind- 
ing gravel  in  the  manner  required  for  water-tight  embankments, 
the  material  being  spread  in  layers  6  to  7  inches  thick  and 
thoroughly  rammed.  The  space  must  be  kept  free  of  water 
while  this  work  is  going  on.  The  filling  must  not  be  reduced 
to  a  semi-fluid  condition,  neither  must  it  be  put  in  in  too  dry  a 
state.  It  must  be  moist  enough  so  that  two  lumps  can  be 
readily  kneaded  together.  It  must  be  brought  fully  up  to  the 
line  of  the  planking  and  trimmed  off,  so  that  the  plank  will 
bear  firmly  on  the  filling  when  they  are  spiked  down. 

The  apron  shown  for  this  dam  is  the  same  as  the  one 
already  described  (Fig.  18),  being  a  platform  of  plank  resting 
on  timbers  which  are  confined  by  long  iron  rods  driven  into 
the  ground.  There  is  no  doubt  that  an  apron  can  be  securely 
confined  in  that  manner.  The  cost  of  the  rods  is  not  serious. 
The  spillway  is  represented  as  200  feet  long,  and  the  fall  is 
8  feet.  Making  the  width  of  the  apron  five  times  the  fall  and 
putting  the  timber's  3  feet  apart  and  the  rods  8,  the  work  would 
call  for  some  320  rods,  costing  a  dollar  or  a  dollar  and  a 
quarter  each — a  trifling  item  in  the  cost  of  such  a  dam.  In  the 
construction  of  such  an  apron  great  care  should  be  taken  to 
make  the  planking  tight,  as  the  impact  of  the  falling  stream 
transmitted  through  any  crevice  in  the  planking  would  tend  to 
cause  a  strong  upward  pressure. 

The  general  method  of  carrying  on  such  a  work  and  con- 
trolling the  water  during  construction  would  be  this:  The 
surface-soil  is  to  be  removed  from  the  entire  area  occupied  by 
the  dam,  and  the  portion  occupied  by  the  spillway  is  to  be 
excavated  to  the  level  oi  low  water.  The  ground  occupied  by 
the  apron  should  be  brought  to  a  level  such  that  there  will  be 
30  inches  of  water  over  it  at  a  low  stage  of  the  stream.  This 
can  be  done  in  low  water,  and  while  the  water  is  warm,  by 
means  of  scrapers,  the  men  and  horses  working  in  the  water. 
After  completion  of  this  excavation  there  will  be  little  current 
in  the  basin  so  formed.  The  apron  can  be  put  together  afloat, 
the  planks  spiked  down  to  the  timbers ;  the  holes  bored  for  the 


4g  CONSTRUCTION  OF  DAMS. 

rods  and  the  latter  inserted;  then  the  platform  weighted  down 
to  the  bottom  and  the  rods  driven  home.  Stone  or  earth  can 
be  used  in  weighting  down  the  apron,  and  left  to  be  swept 
away  by  the  water  after  the  work  is  done.  After  the  rods  are 
driven  down  to  the  water-surface  by  hammers  they  can  be 
driven  home  by  slipping  a  pipe  over  each  rod  and  using  a  long 
heavy  rod,  working  in  the  pipe,  for  a  hammer, 
flows  over  the  apron  during  the  construction  of  the  dam. 

While  the  latter  is  in  progress,  the  stream  is  confined  to  as 
narrow  a  channel  as  it  can  take  without  giving  it  too  high  a 
velocity.     This  channel  may  be  near  one  end  of  the  spillway, 
or  outside  of  the  same  should  the  nature  of  the  ground  admit 
of  that  arrangement.     This  latter  disposition  is  to  be  preferred 
even    should    it   require  some  excavation  to  provide   such    a 
channel,  and  the  raising  of  the  water  3  or  4  feet  to  turn  it  into 
the  same.     In  any  case,  it  is  not  necessary  to  raise  the  water 
till  one  embankment  and  some  two-thirds  of  the  spillway  are 
complete.     In  raising  the  water,  the  row  erf  sheet-piling,   or 
spiling,  along  the  up-stream  face  of  the  spillway  comes  into 
use.     The  arrangement  to  effect  the  raising  of  the  water  is 
precisely  similar  to  that  described  for  the  small  dam,  Fig.  18. 
A  section  of  the  spiling  can  be  driven  below  the  natural  surface 
of  the  water  and  spiked  to  a  mud-sill,  leaving  a  footing  on  the 
mud-sill  for  short  plank  to  join  it  to  the  sill  of  the  dam.      This 
method  does  not  disturb  the  natural  flow  of  the   stream  suffi- 
ciently to  cause  any  scour.     When  the  time  comes  for  raising 
the  water,  short  pieces  of  plank  are  rapidly  inserted  bearing 
against  the  mud-sill  and  spiked  to  the  sill  of  the  dam,  and  a 
bank  of  earth  is  thrown  in  on  the  up-stream  side.     Where  the 
new  channel  reenters  the  stream  a  fall  occurs  and  some  work 
of  protection  is  necessary  to  prevent  the  scour  extending  back 
to  the  dam.     Where  brush  is  plentiful,  as  is  usual  on  the  mar- 
gins  of  streams,    this   is   best  accomplished   by  covering   the 
channel  at  its  infall  with  sink-fascines,  viz.,  loose  stone  enclosed 
in  bundles  of  brush. 

Upon  completion  of  the  spillway,  the  next  step  will  be  to 


DAMS   OF   TIMBER  AND    EARTH.  49 

raise  the  water  still  further  and  throw  it  over  the  latter.  As 
we  are  dealing  with  ground  liable  to  rapid  abrasion,  this  fact 
must  be  kept  in  view  in  all  arrangements  for  controlling  the 
water.  To  attempt  to  stop  the  flow  in  such  a  channel  by  a 
bank  of  loose  stone,  or  by  cribwork  filled  with  stone,  or  by 
bags  of  earth,  is  usually  futile  owing  to  the  rapid  scour  caused 
by  these  obstructions.  Some  preliminary  protection  of  the 
channel  is  indispensable.  Most  naturally  this  protection  takes 
the  form  of  a  thick  brush  mattress  covering  the  bottom  for  a 
length  equal  to  five  times  the  depth  of  water  after  raising,  and 
extending  up  the  slopes  as  high  as  the  water  is  to  be  raised. 
With  this  foundation,  a  bank  of  loose  stone  can  be  thrown  in 
and  backed  by  a  bank  of  earth  with  good  show  of  success. 
The  better  wray,  however,  is  to  provide  the  channel,  before 
admitting  the  water  to  it,  with  a  bulkhead  for  readily  stopping 
the  flow.  Figs.  23  and  24  give  an  idea  of  such  a  bulkhead. 
A  mud-sill  is  imbedded  in  the  bottom  of  the  channel ;  a  row 
of  spiling  driven  'to  a  sufficient  depth,  spiked  to  the  mud-sill, 
and  cut  off  to  leave  a  footing  for  stop-plank.  Uprights  are 
mortised  into  the  mud-sill  and  a  cap  put  on  which  extends 
across  the  channel,  and  is  imbedded  in  the  earth  at  the  sides. 
The  cap  is  well  braced  from  the  bottom  and  sides  of  the 
channel.  When  the  water  is  let  into  the  channel,  it  flows 
gently  over  the  mud-sill  without  causing  any  scour.  When 
the  time  comes  for  raising  the  water,  there  will  be  a  consider- 
able stretch  of  slack  water  above  the  dam,  and  the  stop-plank 
can  all  be  put  in  before  the  water  rises  enough  to  create  any 
serious  scour. 

Where  the  conformation  is  such  that  the  water  cannot  be 
turned  outside  the  spillway,  the  water  is  confined  to  a  narrow 
channel  near  one  end  of  the  latter,  and  flows  there  until  the 
larger  part  of  the  spillway  is  completed  and  planked.  One  of 
the  embankments  may  also  be  fully  completed,  all  the  round 
piles  driven,  and  all  the  sills  put  in  place,  before  turning  the 
water,  but  the  sheet-piling  can  only  be  completed  as  far  as  the 
edge  of  the  stream.  A  gap  cannot  be  left  in  a  line  of  sheet- 


5o  CONSTRUCTION   OF  DAMS. 

piling  to  be  subsequently  closed,  as  the  closure  cannot  be 
effected  with  such  accuracy  as  to  avoid  leakage.  To  finish  the 
dam,  the  water  must  be  excluded  from  the  uncompleted  end 
and  'thrown  over  the  finished  part,  and  room  enough  must  be 
left  to  do  the  work  in  a  proper  manner.  The  best  way  to  do 


\ 


FIG.  23. 


FIG.  24. 

this  is  to  construct  a  wale-and-tie  coffer-dam,  running  up  and 
down  stream,  to  separate  the  completed  from  the  incomplete 
part  of  the  dam.  It  should  lap  on  to  the  dam  as  far  as  the 
crest  and  extend  up  stream  50  feet  or  more.  The  problem 
now  is  to  close  the  channel  between  the  coffer-dam  and  the 


DAMS   OF   TIMBER   AND    EARTH.  5 1 

shore.  There  are  many  ways  of  doing  this :  one  method  being 
the  mud-sill  spiling  and  bulkhead  already  described.  I  will 
detail  a  different  method,  one  which  can  be  rapidly  put  in 
execution,  admitting  the  employment  of  a  large  number  of 
unskilled  workmen.  First,  dig  out  the  channel  to  a  tolerably 
level  bottom  and  steep  bank.  Then  lay  down  a  brush  mat- 
tress extending  across  the  channel  and  some  25  feet  up  and 
down  stream,  weighted  with  stone  or  gravel  to  hold  it  in  place. 
On  the  mattress  set  a  crib  of  open  light  timber-work  held 
together  with  spikes  or  small  drift-bolts  driven  without  boring. 
This  abuts  against  the  coffer-dam  and  reaches  to  the  opposite 
bank,  and  is  weighted  with  stone  to  keep  it  in  place.  This 
will  raise  the  water  a  little,  causing  it  to  flow  through  the 
interstices  of  the  timbers.  Secure  the  shore  end  of  the  crib 
with  a  heavy  bank  of  earth,  and  proceed  to  fill  it  with  stone. 
This  done,  the  water  will  be  raised  several  feet  and  will  con- 
tinue to  flow  through  the  crevices  of  the  stone.  Then  throw  in 
a  heavy  bank  of  earth  above  the  crib.  To  prevent  the  earth 
from  being  washed  through  the  stone,  bundles  of  brush  may 
be  thrown  in  above  the  crib  and  forced  down  with  poles.  The 
water  will  hold  them  against  the  crib  till  the  earth  is  thrown 
in.  Of  course,  during  the  completion  of  the  work,  the  leakage 
through  the  coffer-dam  must  be  removed  either  by  pumping  or 
by  a  siphon  leading  over  the  spillway  and  discharging  below. 

For  a  dam  to  create  water-power,  the  problem  of  control- 
ling the  water  during  construction  is  usually  simpler  than  is 
here  assumed.  In  a  low  stage  of  the  stream  the  water  can 
usually  be  turned  through  the  canals  and  sluices  which  supply 
the  mills.  On  completion  of  the  work  the  closing  of  these 
sluices  turns  the  water  over  the  dam.  This  arrangement  does 
not  allow  coffer-dams  to  be  dispensed  with,  but  it  admits  of 
lower  and  less  expensive  ones.  Permanent  sluices  are  often 
made  in  the  dam  itself  through  which  the  water  flows  during 
construction,  and  which  can  be  closed  by  gates  on  completion 
of  the  work.  Such  an  arrangement  is  imperative  where  the 


j2  CONSTRUCTION  OF  DAMS. 

necessity  exists  for  draining  the  mill-pond,  and  it  is  generally 
advisable  on  account  of  repairs. 

A  pile  dam  similar  in  its  general  features  to  this,  though 
built  with  less  care  than  is  here  contemplated,  was  constructed 
on  the  Cedar  River,  at  Waterloo  in  Iowa,  in  1883,  raising  a 
head  of  some  8  feet.  It  is  still  (1897)  intact,  having  suffered 
no  damage  from  ice  or  floods. 

The  form  of  dam  shown  at  Fig.  25  *  has,  at  present,  a  his- 
torical rather  than  an  engineering  interest.  It  is  the  general 
type  of  dam  adopted  in  the  improvement  of  navigation  on  the 
Muskingum  River  in  the  State  of  Ohio,  in  a  system  of  canals 
and  river  improvement  undertaken  by  that  State  about  1830. 
This  particular  drawing  has  reference  to  the  dam  at  Marietta,  O. , 
where  the  Muskingum  enters  the  Ohio.  The  drawing  of  which 
this  is  a  copy  is  not  accompanied  by  any  explanation  and  must 
be  supplemented  by  the  imagination  of  the  reader.  It  is  pre- 
sumed that  the  timbers  resting  on  the  pile-caps  in  the  apron 
form  a  continuous  flooring,  as  also  the  top  timbers  of  the  step. 
As  to  the  top  of  the  dam  the  drawing  is  manifestly  in  error. 
It  appears  to  show  the  planking  running  lengthwise  of  the  dam, 
which  would  be  a  very  unskilful  arrrangement.  Moreover,  no 
millwright  or  carpenter  would  put  on  the  upper  timbers 
running  to  a  point  in  the  manner  shown.  It  is  probable  that 
the  arrangement  at  the  top  was  something  like  that  indicated 
at  Fig.  25^.  It  is  also  to  be  presumed  that  the  cribwork  was 
filled  with  stone,  and  that  there  were  abutments  of  cribwork. 
It  is  stated  that  a  coffer-dam  of  brush,  stone,  and  gravel  was 
built  preparatory  to  the  construction  of  the  apron,  and  that  the 
cribwork  was  located  thereon.  These  dams  created  falls  of  8 
to  17  feet. 

Fig.  26  represents  a  type  of  dam  said  to  be  much  in  use  on 
the  upper  Allegheny  River  for  falls  of  5  to  8  feet.  This  par- 
ticular sketch  relates  to  the  dam  at  Olean,  New  York.  The 
information  is  derived  from  the  same  source  as  in  the  preceding 

*  Tenth  U.  S.  Census  Report,  vol.  xvn.     The  Ohio  River  Basin,  p.  36. 


DAMS   OF   TIMBER  AND   EARTH. 


53 


m 


111 


__ 


54 


CONSTRUCTION  OF  DAMS. 


DAMS   OF  TIMBER   AND    EARTH.  55 

case.*  Fig.  26  is  compiled  from  the  description,  which  is  not 
accompanied  by  any  drawing.  The  report  is  silent  as  to  the 
apron,  and  an  apron  is  added,  designed  in  accordance  with  the 
general  character  of  the  structure.  For  the  dam,  four  rows  of 
round  piles  are  driven  across  the  stream,  the  piles  being  8  feet 
apart.  Tenons  are  cut  on  the  heads  of  the  piles,  and  caps  are 
secured  to  the  same  by  mortises  and  pins  or  by  dovetailed 
tenons  with  keys  or  wedges.  The  up-stream  row  of  piles  is 
flatted  after  being  driven,  and  planked  down  a  foot  or  two 
below  the  natural  surface  of  the  ground,  the  plank  running 
horizontally.  The  down-stream  row  is  also  flatted  and  planked 
down  to  the  natural  surface.  The  space  between  these  rows 
of  piling  is  filled  with  loose  stone  and  planked  over.  Water- 
tightness  is  secured  by  a  bank  of  earth  thrown  in  above  the 
up-stream  planking.  This  bank  should  preferably  be  earth  of 
a  binding  character,  but  where  a  bank  is  confined,  as  in  this 
case,  a  reasonable  degree  of  water-tightness  can  be  secured 
with  almost  any  kind  of  earth.  The  abutments  of  this  dam 
are  represented  as  of  cribwork,  though  more  properly  they 
should  be  of  stone,  woodwork  above  water  being  liable  to 
rapid  decay.  With  abutments  of  masonry  the  whole  structure 
might  be  considered  as  permanent.  If  the  abutments  are  of 
cribwork  their  faces  toward  the  spillway  must  be  planked, 
although  not  so  represented,  and  the  planking  should  return 
along  the  up-stream  face  and  extend,  as  spiling,  into  the  bank 
of  earth  which  unites  the  abutment  with  the  high  ground. 

As  to  the  order  in  which  the  several  parts  of  this  dam 
should  be  put  in  place,  the  following  observation  may  be  made. 
The  drainage-area  commanded  by  the  dam  is  about  noo 
square  miles.  The  spillway  is  220  feet  long.  We  should 
expect  an  ordinary  low-water  flow  of,  say,  300  cubic  feet  per 
second,  which  would  correspond  to  a  depth  of  6f  inches  on  the 
crest  of  the  .dam.  We  should,  first,  dig  for  the  abutments, 
throwing  up  a  bank  of  earth  and  forming  a  pit  from  which  the 
water  could  be  bailed  if  necessary.  If  the  abutments  are  to 
*  Tenth  U.  S.  Census  Report,  vol.  xvn.  The  Ohio  River  Basin,  p.  n. 


56  CONSTRUCTION  OF  DAMS. 

be  of  stone,  the  pit  should  be  freed  from  water.  If  of  crib- 
work,  it  can  be  dug  2  or  2\  feet  deep  with  shovels  or  scrapers, 
the  lower  timbers  put  together  afloat,  and  as  the  work  pro- 
gresses it  will  settle  firmly  upon  the  bottom.  If  of  masonry, 
the  up-stream  portion  should  be  laid  in  hydraulic  mortar.  The 
apron  must  be  put  in  in  like  manner  by  men  working  in  the 
water,  at  the  lowest  stage  of  the  stream.  The  planking  should 
be  well  below  low  water,  not  only  for  preservation  of  the  timber, 
but  for  moderating  the  shock  of  floating  bodies.  After  driving 
and  capping  the  piles  for  the  spillway,  a  trench  is  dug  along 
the  up-stream  face  as  deep  as  practicable,  the  up-stream  side 
of  the  piles  flatted  and  the  planking  applied.  The  plank  are 
applied  in  this  manner.  Suppose  the  trench  to  be  2  feet  below 
the  natural  surface.  One  tier  of  plank  is  put  in,  forced  down 
to  the  bottom,  and  fastened.  The  earth  is  solidly  packed  on 
the  up-stream  side  of  them.  The  insertion  of  these  plank 
creates  no  scour.  The  second  tier  are  then  put  in,  and  the 
earth  packed  behind  them.  This  will -create  a  slight  fall  and 
tend  to  scour  the  earth  under  the  spillway.  A  layer  of  the 
stone  filling  is  put  in  to  prevent  this.  The  down-stream  plank- 
ing are  put  in  in  like  manner  and  backed  with  earth.  When 
this  is  finished  the  water  is  pouring  over  the  down-stream 
planking  on  to  the  apron.  The  stone  filling  is  thrown  in  and 
brought  up  to  the  proper  level,  the  up-stream  planking  being- 
applied  at  the  same  time.  A  light  bulkhead  is  thrown  up  along 
the  up-stream  face  of  the  dam,  excluding  the  overflow  from  half 
the  length,  while  the  planking  of  the  spillway  is  being  put  on. 
The  bulkhead  is  then  removed  and  applied  on  the  other  half, 
etc.  Another  method  is,  confine  the  flow  of  the  stream  during 
low  water  to  as  narrow  a  channel  as  practicable  near  one  end 
of  the  proposed  dam.  Complete  one  abutment,  and  the 
greater  half  of  the  dam  and  apron,  pumping  for  the  apron  and 
abutment  if  necessary.  Then  raise  the  water  as  above,  throw 
it  over  the  completed  portion,  and  finish  the  rest. 

Other    dams   on   the   same   stream   are   said   to    have   two 
slopes ;  the  up-stream  slope  descending  below  the  natural  bed 


TREE  DAMS,  57 

of  the  stream  and  covered  by  a  bank  of  earth,  forming  a  water- 
tight connection  with  the  bottom.  It  does  not  appear,  how- 
ever, that  this  form  has  any  advantage  either  in  construction 
or  operation. 

Tree  Dams. — Figs.  27  and  28  show  an  example  of  a  tree 
dam,  built  across  Schoharie  Creek,*  in  the  State  of  New  York, 
for  the  purpose  of  diverting  the  water  of  that  stream  into  a 
feeder  of  the  Erie  Canal.  It  is  composed  of  straight  and 
regular  pine-trees,  60  to  70  feet  long,  1 8  to  22  inches  diameter 
at  the  butt,  divested  of  their  branches.  The  butts  of  each  tier 
lay  in  contact,  and  each  tier  is  raised  above  the  one  below  it 
by  a  12-inch  timber.  Each  12-inch  timber  is  drift- bolted  to 
the  tier  of  trees  below  it,  and  receives  the  drift-bolts  which  go 
through  the  tier  above.  The  thickness  of  these  longitudinal 
timbers  combines  with  the  taper  of  the  tree  to  increase  the 
slope  of  each  successive  layer  of  trees.  On  the  upper  layer 
are  bolted  four  12  X  1 2-inch  timbers  supporting  a  flooring  of 
thick  plank.  The  layer  of  brush  and  gravel  which  forms  the 
water-tight  backing  of  the  dam  laps  on  to  the  flooring  and  abuts 
against  a  longitudinal  timber  above  the  planking.  The  abut- 
ments of  the  dam  are  of  masonry  supported  by  piles,  which 
show  in  elevation  in  the  longitudinal  section  Fig.  28,  and  in 
Fig.  27*7.  In  moderate  stages  of  the  stream  the  water  goes 
over  this  dam  in  a  series  of  small  cascades.  In  high  stages 
it  rushes  down  in  an  unbroken  stream. 

The  length  of  this  dam  between  abutments  was  436  feet, 
the  drainage-area  commanded  by  it  being  some  1500  square 
miles.  The  construction  of  the  work  must  have'required  more 
than  1 2OO  trees.  It  is  quite  within  the  limits  of  reason  to  say 
that  this  quantity  of  timber  could  have  been  combined  in  a 
manner  to  form  half  a  dozen  dams  of  the  same  length  and 
height  as  this,  and  built  with  equal  prospect  of  permanence. 
The  great  length  of  abutment  and  retaining-wall  required  in 
this  form  of  dam  is  a  serious  objection.  Another  objection  is: 
The  up-stream  slope  is  so  slight  that  a  sufficient  backing  of 

*  Report  of  the  State  Engineer  of  New  York  for  1865. 


58 


CONSTRUCTION  OF  DAMS. 


TREE  DAMS.  $9 

earth  cannot  be  applied  even  with  the  awkward  expedient  of  a 
timber  running  across  the  planking.  With  a  steeper  slope 
such  an  expedient  would  not  be  necessary. 

This  dam  suffered  considerable  injury  in  the  floods  of 
October,  1869,  and  April,  1870.  In  1871*  it  was  rebuilt  and 
its  length  extended  160  feet,  making  the  overflow  or  spillway 
nearly  600  feet  long.  Figs.  29  and  30  show  the  dam  as 
rebuilt.  The  height  was  reduced  to  three  layers  of  trees 
instead  of  five.  The  down-stream  slope  was  entirely  covered 
with  planking,  and  the  length  of  the  apron  extended.  So  far 
as  can  be  learnt  from  the  reports,  the  dam,  in  this  form,  has 
stood  without  further  injury. 

Fig.  27  shows  the  trees  entirely  divested  of  branches,  while 
in  the  arrangement  of  Figs.  29  and  30  some  branches  remain. 
As  the  first  tier  of  trees  must  be  placed  in  the  water,  it  would 
appear  advisable  to  leave  some  branches  on,  in  order  that  the 
tree  may  be  held  down  by  the  loading  of  stone,  till  the  second 
tier  is  put  in  place.  Fig.  29  shows  the  retaining-wall  extended 
in  the  form  of  a  cribwork  "docking  "  filled  with  stone.  Fig. 
29^  is  a  section  of  the  retaining-wall. 

Fig  3 1  is  a  section  of  the  dam  built  by  the  State  of  Massa- 
chusetts, on  the  Deerfield  River,  about  the  year  1864,  to  furnish 
power,  in  the  form  of  compressed  air,  required  in  the  construc- 
tion of  the  Hoosac  Tunnel,  t  It  is  more  properly  designated  as 
a  log  dam  than  as  a  tree  dam,  being  made  of  round  logs, 
notched  at  their  intersection  and  flatted  to  receive  the  planking. 
The  drainage-area  tributary  to  this  dam  is  234  square  miles  of 
mountainous  country.  The  dam  rests  partly  on  rock  and  partly 
on  gravel,  underlaid  by  rock.  At  one  end  it  abuts  against  a 
precipitous  rock,  at  the  other  against  an  abutment  of  masonry, 
resting  on  gravel  and  faced  with  planking  which  is  fastened  to 
timbers  built  into  the  masonry.  The  spillway  is  250  feet  long, 
being  rather  more  than  I  foot  for  each  square  mile  of  drainage- 

*  Report  of  the  Canal  Commissioners  of  the  State  of  New  York  for  1871. 
f  Tenth  Census  Report  U.  S.,  v.ol.  xvi.   .   Region    Tributary  to  Long 
Island  Sound,  p.  109. 


6o 


CONSTRUCTION  OF  DAMS. 


LOG   DAMS  AND    LUMBERMAN'S  DAMS.  6l 

ground,  whereas  the  Olean  dam  just  described  has  but  I  foot 
to  5  square  miles,  and  the  Schoharie  Creek  dam  I  to  2^. 

On  this  stream  the  ice  sometimes  gorges  and  forms  tem- 
porary dams.  Such  a  gorge,  obliterating  the  fall  at  this  dam, 
is  a  serious  danger  to  be  provided  for,  the  buoyancy  of  such  a 
mass  of  timber  tending  to  lift  and  derange  the  dam.  This 
danger  is  understood  to  be  met  by  a  loading  of  stone,  the 
spaces  represented  as  vacant  being  filled  with  stone. 

Log  Dams  and  Lumberman's  Dams. — The  main  overflow 
shown  at  Fig.  32  is  a  typical  log  dam,  consisting  of  a  cobwork 
of  logs,  supporting  a  deck  of  inclined  planking  or  timber,  one 
end  of  which  projects  over  the  logwork  and  the  other  rests  on 
the  ground  and  is  covered  by  a  bank  of  gravel.  Such  dams 
are  often  built  remote  from  any  source  of  supplies,  with  such 
means  as  can  be  transported  over  very  rough  roads,  in  small 
boats,  or  on  the  shoulders  of  workmen.  Hewn  timber  is  often 
substituted  for  planking,  wooden  treenails  for  drift-bolts  and 
spikes.  The  lumberman's  dams,  so  called,  are  not  always  or 
usually  built  for  purposes  of  power.  They  are  commonly  built 
for  sluicing,  viz.,  to  accumulate  large  volumes  of  water  and 
discharge  it  at  a  very  rapid  rate,  to  facilitate  the  floating  of 
logs.  In  other  cases  they  are  built  to  form  ponds  for  the 
detention  and  sorting  of  logs,  especially  where  the  latter  are 
to  be  made  up  into  rafts.  Fig.  32  *  is  a  cross-section  of  a  dam 
built  for  the  last-named  purpose.  This,  however,  may  be 
taken  as  a  type  of  a  class  of  dams  for  water-power. 

This  dam  is  on  the  Menominee  River,  which  forms  the 
boundary  between  the  States  of  Michigan  and  Wisconsin.  It 
is  near  the  mouth  of  the  river,  about  a  mile  above  the  town  of 
Marinette.  The  site  of  the  dam  is  a  smooth  limestone  rock. 
The  overflow  or  spillway  is  557  feet  long,  the  drainage-area 
being  a  little  over  4000  square  miles.  Unlike  the  Hoosac 
dam,  the  transverse  timbers  are  laid  horizontal,  the  necessary 
slope  being  given  to  the  deck  by  building  the  dam  in  offsets. 

*  Tenth  U.  S.  Census  Report,  vol.  xvn.  Northwestern  Watershed, 
p.  66. 


62 


CONSTRUCTION    OF  DAMS. 


LOG   DAMS  AND   LUMBERiMAN'S  DAMS.  63 

The  deck  is  formed  of  square  timbers  laid  close  together,  the 
ends  which  rest  on  the  bottom  being  overlaid  by  a  bed  of 
gravel  or  earth.  The  lower  log  projects  some  10  feet  beyond 
the  vertical  face  of  the  dam  and  sustains  an  apron,  though  the 
necessity  for  an  apron  on  a  limestone  ledge  is  not  clear.  It  is 
bolted  to  the  rock  by  fox-wedge  bolts  \\  inches  diameter. 
The  timbers  forming  the  body  of  the  dam  are  laid  about  8  feet 
apart  each  way.  This  dam  would  be  greatly  strengthened  by 
a  filling  of  stone.  Constructed  as  represented  it  depends 
wholly  for  its  stability  upon  the  pressure  of  the  water,  and 
would  be  very  readily  destroyed  by  a  gorge  of  ice  or  a  jam  of 
logs  below  it,  such  as  to  obliterate  the  fall.  The  total  cost  of 
this  dam  is  stated  to  be  $10  ooo. 

Fig-  33*  shows  the  rudest  and  simplest  form  of  lumber- 
man's dam  that  the  writer  has  met  with.  It  was  built  by 
lumbermen,  as  a  sluicing-dam,  at  the  outlet  of  Club  Lake,  on 


FIG.  33. 

the  headwaters  of  the  Black  River  in  the  State  of  New  York. 
Fig.  34  shows  the  general  situation  and  a  profile  of  the  stream 
a  little  below  the  dam,  Fig.  34, a.  The  dam  has  no  abutments 
and  takes  its  chance  of  being  flanked.  Being  at  the  outlet  of 
a  series  of  lakes,  the  stream  is  not  subject  to  so  great  fluctua- 
tions as  in  the  ordinary  case.  The  dam  is  267  feet  long  and 
contains  sluices  20  feet  wide,  in  two  sections,  for  discharging 
water  and  logs.  A  foot-path  across  the  stream  is  formed  by 
spiking  to  the  ends  of  the  projecting  logs  upright  plank, 
which  sustain  a  foot-plank  elevated  some  30  inches  above  the 

*  Report  of  the  State  Engineer  of  New  York  for  1888. 


64 


CONSTRUCTION  OF  DAMS. 


crest  of  the  dam.  A  constructive  difficulty  in  this  dam  would 
appear  to  be  the  limited  bearing  which  the  transverse  timber 
has  on  the  longitudinal  timber  at  the  inner  end.  This  can 
be  managed  by  using  larger  logs  next  the  planking  and  notch- 
ing deeply  into  them  for  the  bearing  of  the  transverse  log,  as 
at  a,  Fig.  33.  This  gives  the  bearing  for  the  log  without 
interfering  with  the  bearing  for  the  planking.  No  coffer-dam 
is  required  for  this  work.  The  logvvork  and  sluices  can  be 


FIG.  34. 

built  without  any  sensible  obstruction  of  the  flow  of  the  water. 
The  dam  would  be  the  better  to  be  entirely  filled  with  stone, 
but  in  any  case  a  sufficient  quantity  of  stone  must  be  thrown 
in  to  prevent  rapid  wear  of  the  bottom  during  construction. 
The  bottom  of  the  sluice  is  supposed  to  be  at  the  level  of 
extreme  low  water.  Upon  throwing  in  the  stone,  the  water 
rises  somewhat  and  will  be  partly  flowing  through  the  sluice. 
The  plankwork  is  now  commenced,  starting  at  the  sluice, 
which  should  occupy  the  deepest  part,  and  working  both  ways. 
As  fast  as  the  planking  is  applied  the  earthwork  is  put  in, 
which  closes  the  passage  under  the  plank.  As  the  work  pro- 
ceeds, the  water  rises  more  and  more,  and  when  the  shallower 
parts  of  the  stream  are  reached,  it  is  flowing  wholly  through  the 
sluice.  After  completion  of  the  planking  and  earth  filling,  the 


LOG   DAMS  AND   LUMBERMAN'S  DAMS.  65 

closing  of  the  sluice  causes  the  water  to  rise  and  flow  over  the 
crest. 

Fig.  35  *  is  another  form  of  log  dam,  or  "  spar  dam  "  as  it 
is  more  commonly  called  in  the  lumber  regions,  of  which  there 
are,  or  were  recently,  two  examples  on  the  lower  Fox  River  in 


FIG.  35. 

Wisconsin,  one  at  Appleton  and  one  at  Neenah,  both  on  beds 
of  limestone  rock.  Log  cribs,  8  feet  by  16,  are  placed  in  line 
•on  the  bottom,  with  a  clear  interval  of  8  feet  between  them. 
A  heavy  log  extends  across  the  cribs,  and  on  this  are  laid  one 
•end  of  the  spars,  the  other  end  resting  on  the  bed.  These  are 
hewed  or  sawed  timbers.  Round  timbers  cannot  well  be  used, 
as,  being  smaller  at  one  end  than  the  other,  interstices  must 


FIG.  360. 


FIG.  36. 


exist  too  wide  for  the  security  of  the  earth  filling.  This 
construction  could  not  judiciously  be  applied  to  a  soft  bottom, 
requiring  expensive  arrangements  to  secure  the  cribs  from  being 
washed  out.  Figs.  35  and  36  represent  the  cribs  as  filled  with 
stone,  and  contemplate  the  use  of  mortar  in  the  upper  layers 
to  secure  the  stone  from  being  washed  out  by  the  overflow. 


*  Tenth    U.  S.  Census    Report,    vol.  xvn.     Northwestern   Watershed, 
p.  45- 


66  CONSTRUCTION  OF  DAMS. 

A  better  method  is  to  cover  the  cribs  with  a  decking  of  logs 
confined  by  drift-bolts  as  at  Fig.  36*. 

Fig.  37  shows  a  mode  of  finally  closing  this  dam,  supposing- 
it  to  be  built  without  sluices  or  passages  for  the  water.     In  that 


case,  as  the  sparwork  approaches  completion,  the  water  is 
concentrated  into  a  narrow  gap  through  which  it  pours  with 
great  violence.  The  insertion  of  the  spars,  one  by  one, 
becomes  more  and  more  difficult  and  dangerous,  and  finally 
impossible.  The  case  calls  for  a  method  of  suddenly  closing 
a  gap  of  some  width.  Such  a  method  is  indicated  in  the 
figure.  We  suppose  the  gap  to  extend  from  the  middle  of  one 
crib  to  the  middle  of  the  next,  viz.,  16  feet  in  width.  The 
cross-log  is  placed  in  position  and  confined  as  shown  so  as  to 
be  capable  of  a  slight  movement  of  rotation.  A  light  log  is 
placed  across  the  down-stream  end  of  the  cribs.  The  spars 
for  closing  are  some  16  feet  longer  than  the  others,  and  are 
held  in  a  horizontal  position  by  weights,  one  end  resting  on 
the  down-stream  cross-log,  the  other  in  the  air.  They  are 
fastened  by  drift-bolts  to  the  up-stream  cross-log,  and  to  one 
another  by  planks  and  flatted  timbers,  as  indicated,  forming 
one  great  gate  or  door.  While  resting  in  this  position  the  free 
ends  are  cut  to  the  right  length  and  trimmed  to  fit  the  rock. 
When  the  time  comes  for  closing  the  gap,  stout  ropes  are 
attached  to  the  crib  and  take  a  turn  around  the  flatted  timbers 
on  the  top  of  the  gate,  the  free  ends  in  the  hands  of  workmen. 
The  weights  are  shifted  so  as  to  lower  the  gate,  and  it  is  eased 
down  into  its  position. 


LUMBERMAN'S  DAMS  IN  DEEP    WATER.  67 

Lumberman's  Dams  in  Water  of  Some  Depth. — The  log 

dams  thus  far  described  are  supposed  to  be  built  in  shallow 
water  2\  to  3  feet  deep ;  this  depth  occurring  in  but  a  small 
part  of  the  length.  Even  in  this  depth  it  may  be  sometimes 
advisable  to  put  the  lower  timbers  together,  and  build  up  till 
the  work  rests  on  the  bottom.  When  the  depth  exceeds  3  feet, 
which  it  often  does,  reaching  as  high  as  6  or  even  10  in  places, 
this  mode  of  construction  is  indispensable.  As  an  illustration 
we  take  the  lower  dam  of  the  Menominee  River  Manufacturing 
Company  *  at  Marinette.  This  dam  is  700  feet  long,  resting 
on  a  gravel  bed  and  raising  the  water  7  feet.  In  describing 
the  method  of  construction,  I  use  the  words  of  J.  L.  Greenleaf, 
C.E.,  who  collected  information  as  to  water-power,  etc.,  in  this 
region,  for  the  Tenth  Census.  "  The  method  employed  was  to 
build  the  cribs  over  their  proper  positions  and  sink  them. 
Starting  from  the  Wisconsin  bank,  four  logs  were  floated  down 
into  position  and  held  there,  parallel  with  each  other  and  8  feet 
apart,  with  their  length  in  the  direction  of  the  current.  These 
covered  an  area  45  feet  long  and  32  feet  wide.  Across  these 
was  placed  a  course  of  sawed  timber.  Another  section,  entirely 
similar,  was  floated  down  adjoining  the  first  toward  the  centre  of 
the  river,  but  leaving  a  space  of  8  feet  between  them,  and  across 
these  the  cribwork  was  built  locking  one  with  the  other.  This 
process  of  floating  in  the  sections  and  building  up  the  cribwork 
was  continued,  until  the  position  of  the  runway  was  reached, 
which  was  then  built.  In  sinking  the  cribs,  enough  of  the  sec- 
tions in  the  cribwork  would  be  floored,  so  that  when  filled  with 
stone  the  weight  would  suffice  to  carry  the  structure  down  to 
the  bed,  and  the  other  sections  were  left  open.  When  the 
cribs  were  sunk  in  position,  the  open  sections  were  filled  with 
stone,  which  filled  up  the  irregularities  in  the  bed  under  the 
crib,  and  gave  a  uniform  bearing  to  the  lower  course  of  timber. 
After  completing  the  runway,  a  crib  32  feet  long  was  built  next 

*  Tenth    U.   S.   Census    Report,  vol.    xva.     Northwestern    Watershed, 
p.  67. 


68  CONSTRUCTION  OF  DAMS. 

to  it  on  the  Michigan  side,  and  then  a  space  of  32  feet  was  left 
for  the  passage  of  the  water.  The  process  of  building  the  sec- 
tions and  cribwork  above  them  was  then  continued  to  the 
Michigan  shore.  The  heavy  body  of  water  which  now  passed 
through  the  space  of  32  feet  left  open,  scoured  the  bed  out  to 
a  considerable  depth  before  it  was  closed.  The  method  of 
closing  it  was  to  make  an  immense  trap-door,  with  a  very 
strong  frame,  hung  on  a  horizontal  axis,  and  at  the  proper 
time  this  was  let  down.  The  force  of  the  current  immediately 
forced  it  shut  against  the  cribwork  on  each  side,  and  loads  of 
gravel,  hay,  etc.,  held  in  readiness  were  thrown  in.  And  in 
two  hours  from  the  time  of  starting,  the  opening  was  closed. 
Back  of  this  trap-door  the  cribwork  was  built  up  and  the  dam 
completed. " 

A  more  judicious  proceeding  would  have  been  to  cover  the 
bed  at  the  gap  with  a  strong  mattress,  overlapped  a  little  by 
the  neighboring  cribs  before  concentrating  the  flow  in  it.  The 
runway  referred  to  was  evidently  for  the  purpose  of  discharg- 
ing logs.  The  dam  contained  no  sluice  in  the  sense  of  a 
passage  for  large  volumes  of  water  to  create  a  temporary  rise 
in  the  stream  for  floating  logs.  Such  a  sluice  would  obviate 
the  necessity  for  a  special  passage  for  the  water.  Both  the 
dams  just  described  and  the  dam  of  Fig.  32  were  standing 
intact  in  May,  1898. 

Dams  of  Sawed  or  Hewed  Timber  in  Combination  with 
Earth  or  Loose  Stone. — Pile  and  log  dams  into  which  squared 
timbers  enter  have  already  been  considered.  Dams  of  squared 
timber  without  bearing-piles  may  be  considered  under  two 
general  heads: 

1.  Framed    work    deriving    its   stability   mainly   from    the 
pressure  of  the  water. 

2.  Cribwork  rendered  stable  by  a  filling  of  loose  stone. 
Fig.   38*  represents  a  dam  built  on  the  Kankakee  River 

near  Wilmington,  Illinois,  in    1871,  by  Mr.  E.  S.  Waters,  the 

*  Tenth  U.  S.  Census  Report,  vol.  xvn.  The  Mississippi  River  and 
some  of  its  Tributaries,  p.  113. 


DAMS   OF   TIMBER  AND  'STONE.  69 

engineer  of  the  Kankakee  Company,  a  corporation  organized 
to  construct  and  maintain  works  for  water-power  and  naviga- 
tion on  that  stream.  The  Kankakee  at  this  point  is  a  large 
stream,  having  a  drainage-area  of  over  5000  square  miles.  It 
is  subject  to  some  influences  tending  to  moderate  its  floods,  and 
to  others  tending  to  aggravate  them.  It  issues  from  an  immense 
morass  in  northern  Indiana  called  the  Kankakee  Swamp,  which 
has  considerable  influence  in  steadying  the  flow.  On  the  other 
hand,  its  general  course  is  westerly,  which  tends  to  the 
augmentation  of  floods  by  the  simultaneous  melting  of  snow 
and  breaking  up  of  ice.  For  the  last  25  miles  above  Wilming- 
ton its  course  is  northerly,  tending  to  retard  the  breaking  up 
and  create  ice-jams.  Rises  of  3  or  4  feet  are  common,  and 
floods  of  9  feet  have  been  known.  The  site  of  the  dam  was  a 
limestone  ledge  covered  in  places  with  gravel.  The  dam  was 
1000  feet  in  length,  creating  a  head  of  I  5  feet.  The  dam  con- 
sisted of  a  series  of  frames,  as  indicated  in  the  figure,  6  feet 
apart,  covered  with  planking,  and  backed  on  the  up-stream  side 
with  gravel.  The  sills  and  the  up-stream  rafters,  purlins, 
and  struts  were  12  X  12  inches.  The  down-stream  rafters 
were  10  X  12,  and  purlins  8  X  10.  The  up-stream  planking 
was  3  inches  thick,  down-stream  2.  Each  sill  was  confined 
to  the  rock  by  six  i^-inch  bolts.  The  up-stream  planking, 
it  is  stated,  extended  to  the  rock,  and  the  interstices  were 
closed  with  cement.  Fig.  38  is  taken  from  the  report.  Fig- 
ures a  and  b  are  added  by  the  author. 

It  is  manifest  that,  so  far  as  the  sills  are  concerned,  the 
structure  must  be  very  imperfectly  represented  by  Fig.  38. 
No  rock  bottom  was  ever  so  smooth  and  level  that  such  a  frame 
could  be  placed  on  it  and  bolted  without  some  work  of  levelling 
up.  380,  no  doubt,  represents  the  actual  situation  more 
correctly.  Such  frames  could  never  set  level  without  fitting 
pie'ces  of  timber  to  the  rock  to  form  a  bed  for  the  sills,  or 
building  a  foundation  of  masonry.  It  will  be  perceived  that 
the  down-stream  planking  does  not  extend  to  the  sill.  It  is 
understood  that  it  originally  did  so,  but  that,  dry  rot  appear- 


70  CONSTRUCTION  OF  DAMS. 

ing  a  portion  of  the  planking  was  cut  away,  to  admit  the  air 
under  the  dam.  38^  is  suggested  as  a  better  and  stronger 
arrangement  of  the  framing  for  the  crest  of  the  dam.  It  is 
understood  that  the  purlins  were  bolted  to  the  rafters,  and  it  is 
presumed  that  all  the  members  were  so  connected  to  the  sills 
as  to  prevent  the  lifting  of  the  structure  in  case  of  an  ice-jam 
below,  such  as  to  obliterate  the  fall.  The  lifting  effort  in  that 


jiOFEET 


FIG.  38*5. 

case  might  be  much  greater  than  the  buoyancy  of  the  timber. 
The  jam  and  rise  of  water  is  liable  to  take  place  suddenly. 
The  air  confined  under  the  decks  having  no  opportunity  to 
escape,  the  whole  structure  would  tend  to  rise  like  an  empty 
vessel  submerged. 

In  1883,  the  ice,  being  some  2  feet  thick,  broke  up  and 
aggregated  in  jams  in  the  upper  part  of  the  stream,  remaining 
intact  in  the  reach  immediately  above  the  dam.  In  this  con- 
dition several  days  of  severely  cold  weather  occurred,  and 
broken  ice  froze  together  in  great  masses.  This  was  followed 
by  a  warm  rain  lasting  two  days.  The  ice  moved  down  the 
stream,  breaking  up  the  standing  ice  and  accumulating  in 


DAMS   OF   TIMBER  AND    STONE.  Jl 

masses  which  filled  the  entire  valley.  A  2O-foot  railroad  em- 
bankment is  said  to  have  been  moved  bodily  out  of  line  3 
feet  by  the  ice.  When  this  action  reached  the  dam,  the  ice 
grounded  upon  the  up-stream  slope,  accumulated  to  a  height 
of  20  feet  above  the  crest,  fell  over  upon  the  dam,  and  crushed 
it  like  an  eggshell. 

Framed  dams  on  a  rock  bottom  are  more  commonly  made 
with  but  one  deck,  the  water  falling  freely  from  the  crest.  The 
slope  of  the  deck  is  not  usually  more  than  2  to  i  nor  less  than 
3  to  i .  If  a  dam  depended  wholly  for  its  stability  upon  the 
pressure  of  the  water,  the  former  slope  could  not  be  exceeded 
or  even  closely  approached  without  some  risk  of  sliding.  In 
such  case  the  weight  of  the  dam  cannot  be  considered.  For 
a  slope  of  2  to  i  the  force  tending  to  hold  the  dam  down  is 
twice  that  tending  to  shove  it  down-stream.  A  man  familiar 
with  hauling  heavy  weights  that  drag  on  the  ground  could 
hardly  feel  confidence  in  the  stability  of  such  a  dam.  Never- 
theless accidents  resulting  from  the  sliding  of  such  dams  are 
very  rare,  for  the  reason  that  the  dam  is  hardly  ever  so  situated 
as  to  depend  wholly  upon  the  pressure  of  the  water  for  its 


FIG.  39.  FIG.  390. 

stability,  being  either  bolted  to  the  rock,  backed  with  gravel, 
or  loaded  with  stone, — sometimes  provided  with  all  these 
elements  of  solidity.  The  dam  of  Fig.  33  stood  for  many 
years  with  a  slope  of  2  to  i ,  with  very  little  else  to  confine  it 
than  the  pressure  of  the  water. 

Fig-  39  represents  a  frequent  case  of  a  dam  upon  a  rock 
bottom  of  very  irregular  form,  much  lower  at  the  middle  of  the 


72  CONSTRUCTION  OF  DAMS. 

stream  than  the  sides.  In  this  case  a  cribwork  is  built  up  and 
filled  with  stone  to  the  highest  point  of  the  rock  occupied  by 
the  dam.  This  cribwork  is  surmounted  by  a  framed  dam,  and 
its  width  will  depend  upon  the  height  and  slope  of  the  latter. 
This  was  the  construction  adopted  for  the  dam  of  the  Jackson 
Company  on  the  Nashua  River  at  Nashua,  N.  H.,  near  where 
that  stream  empties  into  the  Merrimac.  The  Nashua  at  this 
point  has  a  drainage-area  of  524  square  miles.  The  dam,  in 
connection  with  a  canal  of  about  1000  feet  length,  creates  a 
fall  of  2 1. 5  feet,  though  the  framed  part  of  the  dam  is  but  little 
over  10  feet  high.  The  sills  are  12  X  15  inches,  the  rafters 
and  struts  12  X  H,  the  purlins  about  n  X  12,  the  frames 
4  feet  apart.  These  dimensions  are  given  from  recollection 
and  may  not  be  quite  exact.  The  spillway  is  1 34  feet  wide, 
and  the  water  has  been  known  to  go  over  it  to  a  depth  of  8  feet 
4  inches.  This  dam  was  built  in  1878  and  has  never  (1898) 
received  any  injury  or  required  any  repairs-,  so  it  is  stated  by 
the  custodians  of  the  dam. 

Cribwork. — Loose  stone,  of  the  kind  usually  available  in 
river  construction,  has  but  slight  stability  against  the  action  of 
running  water.  It  is  true  that  a  mass  of  loose  stone  is  well 
adapted  to  sustain  the  pressure  of  water,  and  a  dam  composed 
of  loose  stone  might  stand  for  some  time  provided  its  crest 
were  at  a  uniform  height.  The  water  flowing  over  it  in  a  thin 
sheet  of  unvarying  thickness  might  not  have  power  to  move 
any  of  the  stones.  The  trouble  with  such  a  dam  is  that  the 
displacement  of  a  single  stone,  by  the  impact  of  a  floating  body 
or  any  other  accident,  is  liable  to  destroy  the  work.  The 
removal  of  a  single  stone  strengthens  the  current  at  that  point, 
and  makes  the  removal  of  the  second  stone  easier,  the  third 
still  more  easy.  Every  advantage  gained  by  the  water 
increases  its  power  for  mischief,  and  it  soon  concentrates  into 
a  torrent  of  irresistible  force. 

The  ease  with  which  heavy  blocks  of  stone  are  moved  by 
a  current  sometimes  appears  incredible.  A  stream  of  water 
impinging  upon  a  flat  surface  perpendicular  to  its  direction 


CRIB  WORK.  73 

exerts  a  pressure  represented  by  twice  the  head  due  the 
velocity,  acting  upon  an  area  equal  to  the  cross-section  of  the 
stream.  The  direct  impact  of  the  water  is  not  the  only  force 
acting  against  the  stability  of  the  stone.  By  reason  of  its 
immersion  or  partial  immersion  in  water,  the  latter  loses  one- 
third  to  one-half  the  weight  of  the  part  immersed.  Moreover, 
on  account  of  the  equal  transmission  of  pressure  in  fluids,  the 
pressure  of  the  impact  acts  often  upon  the  entire  under  side  of 
the  stone  and  exerts  a  strong  tendency  to  lift  it  off  its  bed, 
thus  facilitating  its  movement.*  Stone  used  to  protect  the  bed 
and  banks  of  a  stream  from  the  rush  of  water  occasioned  by  a 
dam,  is  liable  to  the  same  objection.  It  can  be  taken  away 
piecemeal,  stone  by  stone.  It  is  apparent  that  the  application 
of  loose  stone,  so  placed  that  one  stone  derives  no  support  from 
others,  is  very  limited  in  dam  construction,  being  restricted  to 
the  protection  of  earth  from  the  wash  of  a  moderate  current. 
This  object  is  greatly  facilitated  by  the  orderly  arrangement  of 
the  stone,  so  as  to  present  no  projecting  surface  to  the  action 
of  the  water. 

*  The  work  of  Ganguillet  and   Kutter  gives  the  following  formula  for 
the  velocity  required  to  move  stones  or  other  heavy  bodies  : 

v  —  S.blVag (to) 

in  which  v  is  the  velocity  in  feet  per  second,  a  the  mean  diameter  of  the 
body  in  feet,  and  g  its  specific  gravity.  This  formula  is  ascribed  to  Chailly* 
It  assumes  that  the  body  is  immersed  in  water  moving  with  the  velocity  v. 
Some  writers,  by  forgetting  this  condition,  have  made  very  extravagant 
statements.  They  have  found  that  stones,  in  order  to  remain*  permanently 
at  the  foot  of  a  dam,  must  have  a  diameter  more  than  half  the  height  of  the 
dam.  For  a  diameter  of  10  feet  and  specific  gravity  of  2.5  the  above 
formula  gives  v  =  28.35,  being  the  velocity  due  to  a  head  of  12.5  feet.  In 
other  words,  a  stone  to  withstand  the  wash  of  a  dam  12.5  feet  high  must 
have  a  diameter  of  10  feet.  This  statement  would  be  correct  if  we  could 
assume  a  stream  of  water  of  a  depth  equal  to  the  height  of  the  stone, 
moving  with  the  velocity  due  the  height  of  the  dam,  which,  in  the  case 
supposed,  is  an  impossible  assumption.  A  depth  of  4  feet  on  the  crest  of 
a  da'm  would  imply  a  velocity  at  that  point  of  about  n  feet  per  second. 
When  the  sheet  of  water  has  reached  the  bottom  and  attained  a  velocity  of 
28.35  feet  per  second,  it  cannot  have  a  depth  of  more  than  18  or  19  inches, 
and  it  is  only  on  a  portion  of  the  stone  of  this  height  that  the  water  exerts 
a  pressure  represented  by  twice  the  head  due  the  velocity. 


74  CONSTRUCTION  OF  DAMS. 

The  judicious  use  of  random  stone  in  river  work  usually 
requires  them  to  be  confined  so  that  they  cannot  be  separately 
washed  away,  and  can  offer  their  united  weight  against  the 
pressure  of  the  water.  One  of  the  most  common  devices  to  this 
•end  is  cribwork.  A  crib  is  a  great  box  made  of  square  or 
round  timbers,  notched  and  bolted  together,  strengthened  with 
cross-ties,  and  filled  with  stone.  Next  to  mortar  these  are  the 
most  efficient  means  of  uniting  great  quantities  of  stone  into  a 
coherent  mass.  It  is  much  cheaper  for  that  purpose  than 
mortar,  though  that  advantage  is  rapidly  disappearing  through 
increasing  cost  of  timber  and  diminishing  cost  of  cement.  It 
can  often  be  executed  by  sinking  cribs  in  water  where  masonry 
would  require  expensive  coffer-dams.  For  these  reasons  this 
land  of  work  is  still  extensively  used  in  dams. 

Figs.  40  and  41  *  relate  to  a  dam  built  across  the  Merrimac 
River  at  Sewalls  Falls,  near  Concord,  N.  H.  The  river  at  this 
point  has  a  drainage-area  of  about  2350  square  miles.  The 
formation  at  the  site  of  the  dam  is  a  tough  clay  gravel,  called 
by  geologists  "  glacial  gravel,"  underlaid,  at  a  depth  of  10  or 
12  feet,  by  sand.  It  is  in  a  somewhat  rigorous  climate  and 
heavy  ice  is  formed,  although  the  formidable  effects  observed 
in  rivers  running  northward  are  not  to  be  apprehended.  The 
overflow  or  spillway  has  a  length  of  497  feet.  The  dam,  in 
connection  with  a  canal  about  1 300  feet  long,  creates  a  fall  of 
1 6  feet,  which,  it  is  said,  can  by  the  aid  of  flashboards  be 
increased  to  19  or  a  little  more.  It  is  stated  that,  preliminary 
to  the  construction  of  the  spillway,  a  line  of  log  cribs  was 
placed  across  the  stream,  32  feet  apart,  to  support  a  roadway 
for  transport  of  materials,  and  in  part  to  sustain  the  low  coffer- 
dam required  to  turn  the  water  through  the  sluices.  After 
•constructing  the  abutments,  which  were  of  rough  masonry,  the 
spillway  was  put  in  in  sections,  commencing  at  the  abutments 
and  working  toward  the  centre.  The  first  two  sections,  one 
on  each  side  of  the  river,  were  each  about  140  feet  wide  and 
contained  the  sluices  for  discharging  the  water  during  construc- 

*  Engineering  News,  vol.  XXXI.  p.  326;  April  19,  1894. 


CRIB  WORK. 


75 


FIG.  41. 


76  CONSTRUCTION  OF  DAMS. 

tion.  A  general  idea  of  the  nature  of  this  work  can  be  got 
from  the  figure.  It  is  cribwork  formed  of  10-  and  1 2-inch 
square  timbers  laid  up  without  notching  or  locking,  and  con- 
fined with  $-  and  i-inch  square  drift-bolts  20  and  30  inches 
long.  It  forms  a  series  of  pockets,  8  or  10  feet  long  and  7  or 
8  feet  wide,  filled  with  stone  which  is  understood  to  have  been 
packed  by  hand  with  care.  The  crown  and  slopes  were 
covered  with  5 -inch  Southern-pine  planking.  The  level  plat- 
forms, which  receive  the  falling  water,  were  covered  with  steel 
plates  fk  inch  thick.  This  novel  feature  gives  a  peculiar 
interest  to  this  dam,  as  the  greatly  diminished  cost  of  steel  and- 
iron has  of  late  made  such  plates  available  for  use  in  this  class 
of  work.  The  up-stream  crest  of  the  dam  is  also  defended  by 
a  plate  of  the  same  thickness.  The  planks  were  not  laid  in 
contact,  but  with  half-inch  intervals  in  order  to  keep  the  interior 
woodwork  constantly  saturated  with  water.  This  dam  was 
commenced  in  July,  1892,  and  completed  in  August,  1893,  at 
a  cost,  as  is  stated,  of  $175  ooo.  The  general  situation  of  this 
dam  appears  from  the  photograph,  Fig.  42. 

This  dam  depends  for  tightness  wholly  upon  the  row  of 
4-inch  spiling  along  the  up-stream  face.  The  4-inch  line  at 
the  toe  of  the  dam  is  inserted  as  a  guaranty  against  under- 
mining. The  two  intermediate  3-inch  lines  can  hardly  be 
regarded  as  essential.  It  is  understood  that  the  planks  of  this 
spiling  were  not  tongued  and  grooved,  but  merely  jointed  on 
the  edges  in  a  planing-machine. 

During  the  breaking  up  of  the  ice  in  the  spring  of  1895, 
one  of  the  aprons  or  steps  of  this  dam  was  crushed  in  and 
pounded  to  pieces  for  a  length  of  100  feet  and  over.  It  i& 
stated  by  the  superintendent  of  the  works  that  the  water  went 
over  the  dam  during  that  flood  to  a  depth  of  14  feet.  This 
experience  led  to  the  strengthening  of  this  apron  by  the  addi- 
tion of  a  5-inch  layer  of  planking.  The  injury  was  extended 
and  increased  in  1896.  The  abutments,  which  rested  on 
wooden  platforms  on  a  sandy  foundation,  were  very  much 
damaged.  The  easterly  abutment  was  undermined  and  badly 


CRIB  WORK.  79 

tilted,  and  has  since  been  rebuilt.  The  westerly  abutment  was 
also  injured  by  scour. 

The  introduction  of  open  spaces  in  the  deck-plank  of  this 
dam  for  the  purpose  of  keeping  the  timber  wet  is  not  a  feature 
to  be  commended.  It  results  in  a  constant  stream  of  water, 
of  considerable  size,  entering  the  structure  at  the  uper  end,  and 
escaping  at  all  crevices,  near  the  lower  end.  The  wearing 
power  of  such  a  constant  flow  of  water  is  very  great,  and  in  the 
course  of  time  it  is  attended  with  highly  injurious  results  to  the 
timber.  The  maintenance  of  the  timber  in  a  wet  condition 
can  be  secured  by  filling  the  cribs  with  sand  or  gravel  in  addi- 
tion to  the  stone,  so  as  to  form  an  unbroken  mass  from  which 
the  water  does  not  readily  escape.  Then,  however  tight  the 
planking  may  be,  we  may  count  on  the  admission  of  sufficient 
w^ater  to  keep  the  filling  in  a  state  of  saturation. 

The  experience  with  this  dam  clearly  shows  the  inherent 
weakness  of  a  timber  platform  to  sustain  the  impact  of  falling 
masses  of  ice,  especially  where  so  situated  that  there  can  be 
no  depth  of  water  over  the  platform.  The  case  is  very  different 
from,  that  of  Fig.  21,  in  which,  during  the  high  water  accom- 
panying the  breaking  up  of  ice,  the  latter  would  have  to  move 
at  least  12  feet  through  the  water  before  striking  the  bottom, 
and  then  in  an  inclined  direction.  It  has  appeared  to  the 
author  that  there  is  no  inherent  difficulty  in  giving  a  curved 
outline  to  the  descending  face  of  such  a  dam,  and  the  attain- 
ment of  that  object  is  well  worthy  of  study. 

Fig.  43  is  given  with  that  view.  The  arrangement  of  the 
timbers  presents  no  difficulty.  The  only  feature  which  has  in 
any  sense  the  character  of  an  experiment  is  the  bending  of  the 
deck-plank,  an  operation  which,  as  is  well  known,  is  practised 
daily  in  other  lines  of  construction.  The  planking  would  go 
on  in  two  lengths.  The  upper  length  of  16  feet  would  require 
to  be  bent  to  a  versed  sine  of  less  than  18  inches.  The  lower 
length  of  25  feet  would  require  a  versed  sine  of  26  inches. 
There  does  not  appear  to  be  any  difficulty  in  securing  these 
deflections  in  3-inch  plank.  They  are  small  compared  with 


8o 


CONSTRUCTION  OF  DAMS. 


m 


CRIB  WORK. 


Si 


what  is  common  in  ship-building,  and  by  steaming  the  plank 
all  difficulty  would  disappear.  Below  the  inflection-point  of 
the  curved  face  there  would  be  no  harm  in  applying  a  protec- 
tion of  iron,  the  wear  on  that  portion  being  severe.  Strips  of 
flat  iron  3  inches  wide  and  6  or  8  inches  apart  would  be  as 
good  as  continuous  plates.  It  will  be  noticed  in  Fig.  43  that 
we  have  adopted  a  curve  which  leaves  some  16  feet  of  the 
apron  straight  and  level.  Had  we  placed  the  tangent-point  at 
the  lower  extremity  of  the  apron,  we  should  have  had  a  curva- 
ture such  that  the  deflection  of  a  1 6-foot  plank  would  have 
been  less  than  6  inches. 

Fig.  44  is  a  section  of  the  dam  of  the  Wauregan  Mills  *  on 
the  Quinnebaug  River  at  Plainfieid,  Conn.      The  river  at  this 


FIG.  44. 


I  I 


point  has  a  drainage-area  of  something  over  500  square  miles. 
The  spillway  is  350  feet  long.      The  abutments  are  of  rubble 


*  Tenth   U.  S.   Census    Report,  voK   XVI.     Region    Tributary    to    Long 
Island  Sound,  p.  34. 


82  CONSTRUCTION  OF  DAMS. 

masonry  with  dressed  face,  rising  10  feet  above  the  cap  of  the 
dam,  which  is  a  cribwork  of  square  and  flatted  timbers  filled 
with  stone ;  the  timbers  being  laid  about  5  feet  apart  each  way 
and  drift-bolted  at  their  intersections.  The  cap  of  the  dam  is 
about  17  feet  above  the  apron.  Two  features  of  this  dam  are 
to  be  noticed:  (i)  The  up-stream  planking,  which  runs  length- 
wise of  the  dam,  contrary  to  the  usual  practice.  This  disposi- 
tion is  secured  by  means  of  rafters  running  on  the  slant, 
notched  and  drift-bolted  to  the  longitudinal  timbers.  (2)  The 
very  steep  slope  of  the  face,  causing  ice  and  floating  bodies  to 
strike  with  great  force  upon  the  apron,  which  consists  of  square 
timbers  laid  in  contact.  The  angle  of  incidence  being  too 
great  to  permit  falling  bodies  to  glance,  ice  and  logs  must 
strike  with  the  full  force  due  the  head,  the  blow  probably  being 
more  destructive  than  a  direct  one. 

Fig.   45    is  a  study  of  an  arrangement  for  obviating  the 


FIG.  45. 

destructive  action  of  falling  bodies  upon  the  apron,  showing 
how  readily  it  could  be  done  with  the  use  of  iron  plates  applied 
to  curved  planking.  The  inclined  face  joins  the  horizontal 
apron  by  a  curve  of  about  21  feet  radius.  The  transverse 
timbers  of  the  dam  are  extended  and  sustain  longitudinal 


CRIB  WORK.  83 

timbers  cut  to  receive  the  curved  planks.  There  appears  to  be 
no  constructive  difficulty  in  such  an  arrangement,  except  that 
the  radius  is  rather  short  for  plank.  The  dotted  line  shows 
the  curvature  that  would  very  easily  admit  of  applying  plank- 
ing to  the  face.  This  is  a  curve  of  36  feet  radius,  on  which  a 
1 6-foot  plank  would  require  to  be  bent  something  less  than  n 
inches  out  of  line.  With  this  arrangement  the  apron  should 
be  somewhat  extended.  For  the  shorter  radius  it  would  prob- 
ably be  better  to  confine  the  iron  plates  direct  to  the  timbers 
without  the  intervention  of  plank.  Since  the  above  was 
written,  the  author  has  been  informed  by  Mr.  J.  A.  Atwood, 
agent  of  the  Wauregan  Mills,  that  a  portion  of  the  apron 
actually  was  destroyed  in  1893  or  '94.  Mr.  Atwood  says: 
' '  The  bed  of  the  river,  where  the  apron  gave  way,  was  mainly 
•quicksand.  The  part  of  the  apron  which  was  on  a  hard 
bottom  has  remained  in  good  condition.  It  is  certain  that  no 
dam  should  be  built  with  so  steep  a  slope  where  the  foundation 
is  poor. 

Fig.  46  *  relates  to  a  dam  built  about  1 890  on  the  Bear 
River  in  northern  Utah,  some  40  miles  from  the  mouth  of  that 
river  at  Great  Salt  Lake.  Its  purpose  was  to  divert  the  water 
•of  the  river  into  canals  for  irrigation.  It  has  an  overflow  370 
feet  in  length,  discharging  the  drainage  of  6000  square  miles  of 
mountainous  country,  though  the  stream  does  not  appear  liable 
to  great  floods.  The  average  monthly  flow  from  1889  to  '92 
did  not  exceed  5500  cubic  feet  per  second,  though  this  figure 
may  have  been  greatly  exceeded  for  some  days.  In  June, 
1 894,  t  the  flow  reached  8000  cubic  feet  per  second.  The  dam 
is  a  cribwork  made  of  10  X  12  squared  timbers,  except  the 
bottom  sills,  which  are  12  X  12.  These  sills  are  bolted  to  the 
rock  bottom  by  i^-inch  anchor-bolts  3  feet  long,  four  to  each 
sill,  confined  by  fox-wedges.  The  three  lower  courses  of 
transverse  timbers  are  horizontal.  Above  these  the  timbers 

*  Engineering  News,  New  York,  vol.  xxxv.  p.  83. 

f  Eighteenth  Annual  Report  of  the   U.  S.  Geological  Survey,  Part  IV, 
p.  321. 


84  CONSTRUCTION  OF  DAMS. 

are  inclined  at  an  angle  of  30°,  giving  the  down-stream  face 
an  angle  of  60°  with  the  horizontal  and  forming  a  right  angle 
at  the  summit.  The  timbers  are  fastened  to  each  other  by 
drift-bolts,  and  the  internal  spaces  filled  with  stone.  The  sills 


FIG.  46. 


extend  7  feet  10  inches  beyond  the  foot  of  the  face-slope,  and 
are  planked  to  form  an  apron  for  the  protection  of  the  bottom. 
The  rear  slope  of  the  dam  is  covered  with  two  layers  of  2 -inch 
planking;  the  front  slope  with  one  layer  of  3-inch.  The 
up-stream  v&rtical  face  has  a  single  layer  of  3 -inch  plank.  A 
heavy  bank  of  earth  closes  all  interstices  on  the  up-stream  side. 
The  dam  joins  steep  escarpments  of  rock  on  either  end,  and 


CRIB  WORK.  85 

no  artificial  abutments  were  required.      The  photographic  view 
Fig.  47  shows  the  general  situation  of  the  dam. 

The  section  exhibits  the  dam  resting  upon  firm  rock.  This 
was  the  fact  for  the  greater  part  of  its  length ;  but  some  i  oo 
feet  of  the  westerly  part  rested  on  gravel  and  boulders,  through 
which  the  water  found  its  way,  and  in  1891,  soon  after  raising 
the  water,  the  river  was  found  running  mainly  under  the  dam, 


FIG.  47. 

instead  of  over  it.  The  breach  was  temporarily  stopped  with 
brush  and  gravel,  and  on  recurrence  of  low  water  a  concrete 
wall  was  inserted  reaching  down  to  rock,  and  the  dam 
reinforced  with  boulders  and  backed  with  gravel,  at  a  cost  of 
some  $5000.  It  is  understood  that  no  further  trouble  has 
occurred. 

The  general  drainage-basin  of  Bear  River  is  north  of  latitude 
42  and  some  6000  feet  above  the  sea-level.  It  is  presumable 
that  heavy  ice  must  occur.  The  apron  if  constructed  as  indi- 
cated appears  to  be  a  very  inadequate  safeguard  for  such  an 
emergency,  especially  for  the  .portion  resting  on  gravel. 

The  largest  dam  of  cribwork  in  this  country,  perhaps  the 
largest  in  any  country,  is  the  dam  of  the  Holyoke  Water-power 
Company,  on  the  Connecticut  River,  at  Holyoke,  Mass.,  where 
that  stream  has  a  drainage-area  of  8000  square  miles.  The 


86  CONSTRUCTION    OF  DAMS. 

history*  of  this  dam  is  obtainable  from  authentic  sources,  and 
it  is  believed  that  it  will  be  instructive  to  give  it  in  some  detail. 

A  timber  dam  was  built  across  the  Connecticut  at  Holyoke 
in  1848,  of  a  much  less  substantial  construction  than  the  one 
here  called  the  crib  dam.  It  was,  as  is  stated,  only  expected 
to  maintain  a  head  of  water  for  a  few  years,  and  then  to  serve 
as  a  coffer-dam  for  a  more  substantial  structure.  No  plan  or 
description  is  extant  from  which  the  details  of  this  dam  can  be 
learnt.  It  is  said  to  have  had  a  base  of  60  feet,  with  a  height 
of  30,  and  to  have  been  nearly  vertical  on  the  face.  It  was 
completed  in  November,  1848,  and  the  gates  were  closed  to 
raise  the  water  on  the  sixteenth  of  that  month,  there  being 
then  a  considerable  rise  in  the  river.  When  the  water  had 
risen  to  within  2  or  3  feet  of  the  top,  the  greater  part  of  the 
dam  rolled  over  and  was  carried  away. 

It  would  be  interesting  to  know  the  exact  construction  of 
this  dam,  and  consequently  the  precise  reason  for  its  failure. 
A  structure  which  fails  is  often  more  instructive  from  an 
engineering  point  of  view  than  the  one  which  stands ;  but  it  is 
not  at  all  likely  that  any  plan  of  the  work  was  ever  made.  It 
is  quite  conceivable .  that,  through  defects  in  construction  or 
design,  the  water  came  to  full  pressure  within  the  dam,  i.e., 
that  the  down-stream  face  held  the  water  instead  of  the  up- 
stream. This  would  relieve  the  slant  face  of  the  pressure 
tending  to  hold  the  dam  down,  and  leave  it  free  to  turn  over 
under  the  pressure  acting  on  the  down-stream  face. 

The  crib  dam  was  commenced  and  finished  in  the  summer 
of  1849.  It  is  a  cribwork  of  square  timber,  mainly  12  X  12, 
put  together  as  shown  in  section  in  Fig.  48.  The  transverse 
timbers  are  6  feet  apart  and  slope  at  an  angle  of  2i|°  with  the 
horizontal,  about  2£  base  to  i  perpendicular.  The  lower  ends 
of  these  timbers  were  bolted  to.the  rock  by  fox-wedge  belts, 
of  which  it  is  stated  that  3000  were  used.  The  back  slope  was 
covered  with  6-inch  hemlock  planking  and,  toward  the  crest, 
by  two  and  even  three  layers  of  the  same.  The  crest  was  pro- 
*See  Transactions  of  the  Am.  Soc.  of  C.  E.,  vol.  xv.  Paper  No.  339. 


CRIB  WORK. 


88  CONSTRUCTION  OF  DAMS. 

tected  by  sheets  of  boiler-plate.  The  abutments  were  of 
masonry  and  were  very  massive.  A  massive  bulkhead  or  gate- 
house adjoins  the  canal  and  controls  the  flow  of  water  into  the 
system  of  canals ;  but  this  is  not  reckoned  as  a  part  of  the 
dam.  The  rollway  of  this  dam  was  1017  feet  long. 

In  the  construction  of  this  dam  a  low  coffer-dam  was  built 
to  exclude  the  water  from  half  the  site  of  the  dam.  This 
portion  was  commenced,  raised  above  the  ordinary  water-level, 
and  provided  with  sluices  through  which  the  water  was  turned 
when  work  was  commenced  on  the  other  half.  The  com- 
mencement of  the  work  was  the  bolting  of  three  1 5 -inch  square 
timbers  to  the  rock  at  the  foot  of  the  down-stream  face  (see 
Fig.  48).  These  timbers  were  level  in  the  longitudinal  direc- 
tion ;  their  upper  faces  were  in  line  with  each  other  and  inclined 
transversely  at  the  angle  of  the  slope,  viz. ,  2 1 1°.  This  formed 
the  starting-point  of  the  work.  The  short  transverse  timbers 
were  laid  on,  6  feet  apart,  bolted  to  the  rock,  and  drift-bolted 
to  the  1 5 -inch  timbers;  then  a  set  of  longitudinal  timbers, 
then  a  set  of  transverse  timbers,  etc.  The  whole  was  filled  to 
a  depth  of  10  feet  with  stone.  Where  the  planking  joined  the 
rock,  at  the  foot  of  the  up-stream  slope,  a  small  bank  of  con- 
crete was  deposited.  A  bank  of  gravel  was  deposited  at  the 
foot  of  the  up-stream  slope,  extending  70  feet  up-stream  and 
30  feet  or  more  up  the  slope.  This  bank  was  extended  later. 
The  gates  were  closed  October  22,  1849,  and  the  water  rose 
and  flowed  over  the  dam.  These  gates  were  merely  portions 
of  the  planking  joined  together  and  provided  with  hinges. 
They  were  46  in  number,  measuring,  each,  18  feet  lengthwise 
of  the  dam  and  18  feet  on  the  slant  side,  occupying,  with  the 
necessary  intervals  between  them,  the  entire  length  of  the  dam. 
The  lower  edge  of  the  gate-opening  was  on  a  level  with  the 
top  of  the  stone  filling.  During  the  construction  of  the  dam 
the  gates  were  held  open  by  props.  On  completion,  a  man 
was  stationed  at  each  gate  and,  on  a  signal  from  the  engineer, 
the  props  were  knocked  away  and  the  gates  fell  simultaneously. 
November  I2th,  following,  a  very  striking  phenomenon  was 


CRIB  WORK.  89 

developed  which  has  ever  since  been  a  subject  of  scientific 
curiosity.  The  water  going  6  feet  deep  over  the  dam,  the  fall- 
ing sheet  vibrated,  and  communicated  vibrations  to  the  air,  at 
the  rate  of  128  per  minute.  So  strong  were  these  vibrations 
that  windows  at  Springfield,  8  miles  distant,  rattled  in  harmony 
with  the  vibrations  of  the  water.  The  maximum  depth  on  the 
dam  occurred  in  April,  1862,  when  the  water  stood  12  feet 
6  inches  deep  on  the  crest.  This  was  2  feet  6  inches  more  than 
had  been  assumed  in  the  design  of  the  work,  and  necessitated 
the  raising  of  the  abutments  and  gate-house.  This  height  of 
12  feet  6  inches  would  indicate  more  than  140000  cubic  feet 
per  second  going  over  the  dam,  being  at  the  rate  of  17  or  1 8 
cubic  feet  per  second  for  each  square  mile  of  drainage-ground. 
Depths  as  great  as  9  feet  on  the  dam  have  occurred  several 
times. 

This  dam  stood,  in  the  form  of  Fig.  48,  some  twenty  years, 
during  which  time  forces  were  continually  at  work  threatening 
its  ultimate  destruction.  It  stood  upon  a  ledge  of  red  slate 
interspersed  with  seams  of  cleavage  which  dip  down-stream  at 
an  angle  of  30°  with  the  horizon.  The  texture  of  the  stone 
not  being  of  the  hardest,  and  the  direction  of  the  falling  stream 
such  as  to  cause  immense  pressure  in  any  open  seams,  a  rapid 
abrasion  of  the  bed  ensued.  By  the  year  1866  this  had  become 
threatening.  A  pit  more  than  20  feet  deep  had  been  exca- 
vated below  the  dam  and  was  extending  up-stream.  Another 
agency  of  destruction  had  also  become  formidable.  Logs  and 
heavy  blocks  of  ice,  falling  over  the  dam,  were  caught  in  the 
rolling  eddies  which  are  always  set  up  when  a  stream  of  water 
falls  into  a  pool,  and  battered  against  the  face  of  the  dam. 
Logs  were  especially  harmful,  for  they  often  struck  the  dam, 
head  on,  with  such  force  as  to  wedge  themselves  between  two 
horizontal  timbers,  where,  the  outer  ends  being  acted  on  by 
the  water,  they  exerted  a  leverage  which  no  strength  could 
resist. 

In  1868  it  had  become  apparent  that  immediate  measures 
were  necessary  to  save  the  dam,  and  the  company  commenced 


90  CONSTRUCTION  OF  DAMS. 

the  construction  of  the  crib  apron  shown  in  Fig.  480.  This 
was  made  of  round  logs  6  feet  apart  each  way,  notched  together 
and  fastened  by  drift-bolts  and  filled  with  stone.  The  part 
under  water  was  built  in  separate  cribs,  each  about  150  feet 
long  and  50  feet  wide,  built  afloat,  floated  into  position  and 
sunk.  During  such  work,  the  sheet  of  water  coming  over  the 
dam  was  confined  to  one-half  the  latter  by  flashboards,  allow- 
ing work  to  go  on  upon  the  other  half.  The  work  being  done 
in  a  low  stage  of  the  stream,  this  was  easily  managed.  The 
superstructure  of  the  apron,  or  part  of  it  above  water,  was 
built  continuously,  without  reference  to  the  length  of  the 
separate  cribs,  so  that  the  work  consisted  of  a  series  of  cells  or 
pockets  6  feet  square,  less  the  thickness  of  the  logs.  These 
cells  were  filled  solid  with  stone  to  the  top  and  planked  over 
with  6-inch  hard-wood  plank.  The  apron  was  commenced  in 
1868  and  finished  in  1870. 

With  this  reinforcement,  the  dam  stood  satisfactorily  for 
nearly  ten  years,  but  about  1 879  new  signs  of  weakness  began 
to  appear. 

It  was  confidently  predicted  by  the  builders  of  the  dam 
that  the  work  was  practically  indestructible.  They  say  in  a 
pamphlet  calling  attention  to  their  enterprise,  in  1853:  "The 
firm  basis  upon  which  the  dam  stands,  ...  the  strength  and 
solidity  of  the  structure,  .  .  .  the  thick  bed  of  gravel  on  the 
upper  end  of  the  dam,  .  .  .  the  substantial  manner  in  which  the 
work  was  executed,  .  .  .  the  effect  of  the  water  upon  the 
material  of  which  it  is  constructed  rendering  it  practically 
indestructible  .  .  .  These  things  leave  no  room  for  doubt  as 
to  its  permanence  and  security."  Again,  a  contemporary 
publication  says:  "The  dam  leaks  a  little,  but  .  .  .  this  is 
considered  no  fault,  as  a  sufficient  leak  is  necessary  to  keep  all 
the  timbers  bathed  in  water  to  prevent  rot. ' ' 

In  adopting  this  opinion  as  to  the  preservation  of  the  timber  - 
work,  the  promoters  of  the  enterprise  committed  an  error. 
Timber  immersed  in  water  does  not  decay,  for  the  reason 
that  the  water  excludes  the  air.  It  is  a  mistake  to  suppose 


CRIB  WORK.  pi 

that  keeping  timber  sprinkled  or  moistened  with  water,  without 
excluding  the  air  from  it,  will  prevent  decay.  It  is  conceiv- 
able that  a  stick  of  timber  in  the  dam  might  be  so  thoroughly 
bathed  with  water  by  leakage  as  to  arrest  decay,  but  this  is  a 
condition  which  cannot  be  expected  generally.  Many  parts 
of  the  dam  must  be  in  a  state  not  wet,  but  simply  moist,  that 
is,  in  a  condition  eminently  favorable  to  decay,  air  and  moisture 
being  the  twin  agents  of  decomposition.  Another  error  was 
committed  in  using  hemlock  for  the  exterior  planking,  that 
timber  being  very  perishable  under  the  influence  of  air  and 
moisture. 

In  1879  a  whirling  vortex  appeared  in  the  surface  of  the 
water  over  the  up-stream  slope  of  the  dam,  indicating  the 
passage  of  water.  Examination  disclosed  a  break  in  the 
planking  at  this  point.  A  very  simple  and  effective  expedient 
was  adopted  to  repair  this  and  subsequent  breaks.  A  coffer- 
dam of  cribwork  was  made  in  the  form  of  a  box  open  at  top  and 
bottom.  The  top  was  square  to  the  axis,  and  the  bottom 
inclined  at  an  angle  equal  to  the  slope  of  the  dam,  so  that 
when  resting  on  the  dam  the  top  was  level.  This  was  floated 
into  position  and  placed  on  the  dam  so  as  to  surround  the 
break.  As  soon  as  a  water-tight  connection  was  formed 
between  the  crib  and  the  dam,  the  water  disappeared  from  the 
former,  passing  through  the  break  in  the  planking,  and  men 
were  able  to  enter  the  crib  and  remove  and  renew  the  defective 
planking.  This  method  was  by  no  means  so  easy  of  applica- 
tion as  it  appears.  The  back  of  the  dam  was  originally 
covered  to  the  height  of  30  feet  from  the  foot  of  the  slope  with 
gravel  in  which  huge  boulders  were  imbedded.  The  remainder 
of  the  slope  had  in  the  course  of  years  become  covered  many 
feet  in  depth  with  sediment  and  river  gravel  containing  trunks, 
branches,  and  roots  of  trees,  which  from  long  immersion 
become,  so  to  speak,  "water-logged"  and  do  not  float,  but 
roll  along  the  bottom  till  arrested  by  some  obstacle.  Different 
methods  of  removing  these  deposits  were  tried.*  A  jet  of 

*  It    is  probable  that  a  15-    or  iS-inch  centrifugal    pump    driven    by  a 


92  CONSTRUCTION  OF  DAMS. 

water  playing  through  a  nozzle  directed  by  a  diver  was  effec- 
tive, but  slow.  A  road-scraper  operated  by  lines  from  an 
anchored  boat,  and  attended  by  a  diver,  was  more  satisfactory, 
but  was  attended  with  no  little  danger  to  the  diver,  viz.,  there 
was  no  telling  when  he  might  encounter  a  spot  in  the  planking 
just  ready  to  break  through,  in  which  event  he  would  almost 
inevitably  be  drawn  into  the  opening.  One  diver  was,  in  fact, 
lost  by  being  drawn  into  an  unsuspected  opening  in  the  dam. 

These  breaks  became  alarmingly  frequent  in  the  succeeding 
years,  and  in  1884,  under  direction  of  Mr.  Clemens  Herschel, 
then  engineer  of  the  company,  comprehensive  and  systematic 
repairs  were  undertaken.  The  water  was  excluded  by  the 
methods  already  described  and  by  analogous  methods.  Much 
of  the  planking  was  found  entirely  decayed  except  a  very  thin 
crust  of  the  upper  surface,  a  result  which  should  have  been 
foreseen,  since  the  under  surface  of  the  planking  could  by  no 
possibility  be  maintained  in  a  condition, to  exclude  the  air. 
The  timber  was  in  a  better  state  of  preservation,  and  only  a 
small  portion  near  the  crest  required  renewal.  The  planking 
was  wholly  renewed  above  the  level  at  which  water  stood 
within  the  dam.  A  diaphragm  of  3 -inch  planking  was  inserted 
within  the  dam,  extending  from  one  abutment  to  the  other,  and 
from  the  crest  to  a  level  25  to  28  feet  below  the  same.  The 
dam  never  having  been  entirely  filled  with  stone,  and  much  of 
the  original  filling  having  been  washed  out,  the  filling  was 
completed,  not  with  stone,  but  with  gravel.  After  the  comple- 
tion of  these  repairs,  in  1885,  the  dam  appeared  to  be  as  good 
as  new,  and  showed  no  further  indication  of  weakness.  In 
1895  the  company  commenced  the  construction  of  a  massive 
stone  dam,  to  replace  the  one  whose  history  we  have  been 


powerful  stearr.-engine,  pump  and  engine  mounted  on  a  flat  boat,  throwing 
a  stream  of  30  cubic  feet  per  second  at  a  high  velocity,  would  have  been 
an  efficient  means  of  removing  these  deposits. 

*The  facts  relating  to  the  Holyoke  dam  are  taken  mainly  from  Clemens 
Herschel's  paper,  No.  339,  in  Trans.  Am.  Soc.  C.  E.,  1886. 


CHAPTER    IV. 
DAMS  OF   MASONRY. 

A  DAM  is  ordinarily  intended  or  desired  to  be  a  permanent 
structure.  The  same  reasons  which  lead  to  its  construction 
demand  its  continued  existence.  Dams  of  timber  and  earth  or 
timber  and  loose  stone  can  only  be  regarded  as  temporary. 
They  either  decay,  wear  out,  or  are  destroyed  by  floods  in  a 
limited  number  of  years.  Such  dams  have  played  an  important 
part  in  the  development  of  industry  hitherto,  and  will  continue 
to  do  so  in  future ;  but  there  is  a  constantly  increasing  demand 
for  permanence  in  this  class  of  structures,  and  we  may  look 
with  confidence,  in  the  future,  for  a  constantly  increasing  pro- 
portion of  masonry  dams.  This  expectation  is  founded  upon 
these  considerations: 

1.  The  increasing  cost  of  timber. 

2.  The  diminishing  cost  of  masonry. 

3.  The  greatly  diminished  rate  of  interest. 

The  increase  in  cost  of  timber,  though  very  decided,  is  not 
so  great  as  might  have  been  expected.  Accessible  forest  lands 
have  been  stripped  of  timber,  or  have  greatly  increased  in  price, 
and  resort  is  had  to  distant  lands;  but  these  tendencies  are 
largely  counteracted  by  the  great  improvements  that  have 
taken  place  in  means  of  manufacture  and  transportation. 
Moreover,  the  stripping  of  timber  from  forest  lands  does  not 
destroy  its  power  of  reproduction.  Timber,  although  a  crop 
of  slow  growth,  is  none  the  less  a  usufruct  of  land,  which  comes 
to  maturity  in  due  time,  and  the  increased  attention  now  being 
directed  to  the  care  and  preservation  of  forests  will,  it  is  to  be 
hoped,  insure  reasonable  supplies  in  future. 

*  93 


94  DAMS   OF  MASONRY. 

The  diminution  in  the  cost  of  masonry  is  more  marked  than 
the  increase  in  the  cost  of  timber.  The  steam-drill,  steam- 
hoisting,  channelling  and  dressing  machinery,  improved  ex- 
plosives, lower  rates  of  transportation,  have  not  failed  of  their 
due  effect  upon  this  branch  of  industry.  Improvements  in  the 
manufacture  of  cement,  also,  have  diminished  the  cost  of  this 
element.  These  tendencies  have  been  partly  met  by  higher 
rates  of  wages,  but  the  net  result  is  a  material  diminution  in  the 
cost  of  masonry. 

The  rate  of  interest  in  the  United  States  may  be  fairly 
stated  to  have  diminished  by  one-half  since  1850.  At  that 
time,  the  United  States  government,  rich  corporations,  and 
prosperous  municipalities  in  the  older  parts  of  the  country  paid 
6  per  cent  for  money,  while  in  the  newer  parts  fabulous  rates 
prevailed,  12  per  cent  being  no  uncommon  rate  on  municipal 
bonds  of  undoubted  validity.  At  present  the  United  States 
government  and  the  State  and  municipal  governments  have 
no  difficulty  in  borrowing  at  3  per  cent. 

It  may  be  worth  while  to  introduce  here  certain  simple 
formulas  in  regard  to  computation  of  interest. 

Let  P  represent  a  principal  or  sum  placed  at  interest  or 
payable  at  a  future  time,  r  the  rate  of  interest,  n  the  term  of 
years  considered.  Then  the 

Amount  of  P  at  the  end  of  I  year  is  P(i  -\-  r} ; 

3    "     «     P(i  +  r)*  ;  etc. 
Amount  at  the  end  of  n  years  is         P(i  -(-  r)H. 

Call  Pl  the  present  value  of  P  dollars  due  in  n  years,  r 
being  the  annual  rate  of  interest.  Then 

Pl(i+ry  =  P,     whence 

Let  P2  represent  the  sum  of  money  which,  at  the  rate  r, 
will  produce  P  dollars  at  the  end  of  every  period  of  n  years, 
in  perpetuity. 


COMPARATIVE   COST  OF  CONSTRUCTION.  95 

We  must  have     P2(i  -f-  r)"  =  P  +  P2  ,     or 

AK1  +>-)"-  01  =  ^. 

whence 


An    annual   payment  of  P  dollars  running  for  n  years  at 
the  rate  of  interest  r  : 

The  first  payment  amounts  at  the  end  of  n  years  to  P(i  -f-  r)M  ', 
second      "  "  "          "          "      "      P(i+r)"-1; 

third         "  "  "          "          "      "  /'(i-fr)"-2,  etc. 

The  last  payment,      "  "          "          "      "    P(i  -f  r). 

The  tota!5  =^{(i  +  r)*+(i  -f-  r)-'  +  etc.  +  (i+'r)}. 

Multiply  this  series  by  -  —  —  .     This  does  not  alter 

Its  value,  but  reduces  its  form  to 


This  is  for  the  case  in  which  the  first  payment  is  made  at 
the  beginning  of  the  first  year,  and  the  nth  or  last  payment 
at  the  beginning  of  the  last  year.  If  the  first  payment  were 
made  at  the  end  of  the  first  year  and  the  last  at  the  end  of  the 
last  year,  the  result  would  be 


These  results  may  be  made  equally  applicable  when  the 
Interest  period  is  other  than  a  year,  as  a  quarter,  a  month,  etc., 
by  adopting  the  proper  values  for  r  and  n.  Thus  in  (14)  if  the 
term  of  years  is  30  and  the  rate  of  interest  is  6  per  cent  per 
annum,  but  payable  monthly,  the  formula  would  be 

.  (..005)*-,    .  . 

0.005 

To  those  who  prefer  graphic  methods  the  diagram  Fig. 
49  will  be  interesting.  Let  CA  represent  a  sum  of  money. 
Draw  A  \  perpendicular  to  CA  and  make  its  length  such  that 


96  DAMS   OF  MASONRY. 

Ci  =  the  amount  at  the  end  of  i  year  at  the  assumed  rate  of 
interest,  i.e.,  Ci  =  CA(\  -j-  r}.  Then  draw  12,  23,  34, 
etc.,  respectively  perpendicular  to  Ci,CA.  €2  will  be  the 


FIG.  49. 

amount  at  the  end  of  two  years,  CT>  at  the  end  of  three,  etc. ; 
Cn  at  the  end  of  n  years.  In  like  manner  draw  Aa,  ab,  be, 
cd,  etc.  Ca  will  be  the  present  value  of  the  sum  due  one 
year  hence,  ab  the  present  value  due  in  two  years,  be  due  in 
three,  cd  due  in  four,  etc.,  at  same  rate  of  interest.  Annuities 
can  be  summed  up  with  a  pair  of  dividers,  as  the  reader  \vill 
readily  perceive. 

Let  us  now  see  how  these  considerations  would  affect  the 
choice  between  a  masonry  and  a  timber  dam,  fifty  years  ago  as 
compared  with  the  present  time.  We  will  take  as  an  example 
the  dam  built  at  Holyoke  in  1849,  an<^  we  W'H  proceed  upon 
the  following  assumptions: 

1.  That  a  timber  dam  with  a  suitable  apron,  to  avoid  the 
great  expense  of  1868,  might  have  been  built  in    1849  f°r 
$300000,  and  we  will  assign  $2000  per  annum  as  the  cost  of 
maintaining  the  dam. 

2.  That  the   duration   of  such   a   dam    might  have  been 
assumed  at  fifty  years,  and  that  the  average  rate  of  interest 
during  that  period  might  have  been  taken  at  6  per  cent. 

3.  That  a  masonry  dam  to  last  indefinitely,  without  repairs,, 
would  have  cost  $800000. 

On  this  basis  how  would  the  question  have  stood  in  1 849  ? 
$800000  at  6^  would  amount  in  50  yrs.  to  $14736000 

$300000        "        "          "        "         "    $5  526  100 
$2000  per  an.        "         ««       "         ««       $615520 
Rebuilding  dam  at  end  of  50  years             $350  ooo — $6  491  620 
Balance  in  favor  of  timber  dam $8  244  380 


COMPARATIVE    COST  OF  CONSTRUCTION.  97 

So  that  if  the  company  in  1849  had  been  possessed  of 
$800000  applicable  to  the  building  of  a  dam,  and  could  have 
been  assured  of  6  per  cent  per  annum  during  the  ensuing  period 
of  fifty  years,  by  adopting  a  wooden  dam  they  might,  in  addi- 
tion to  having  a  new  dam  at  the  end  of  that  period,  have  been 
better  off  by  8J  millions. 

Ho\v  would  the  question  stand  at  present  ?  We  may 
assume  that  a  substantial  dam  of  masonry  could  be  built  now 
for  $550000,  and  that  not  more  than  3  per  cent  can  be 
obtained,  as  an  average,  on  large  sums  of  money  during  the 
next  fifty  years.  We  will  take  the  present  cost  of  a  timber 
dam  at  $350000,  and  the  annual  repairs  at  $2000,  as  before. 
$550000  at  3$  amounts  in  50  years  to. .  .  $2411  140 

$350000  "  "  "  $i  534350 
$2000  per  annum  "  "  "  "  $232360 
Rebuilding —  $350000  $2  116710 

Balance  in  favor  of  timber  dam $294430 

The  computation  still  shows  in  favor  of  a  timber  dam,  but 
the  advantage  is  slight  compared  with  that  of  1 849. 

In  the  ordinary  case,  and  especially  on  a  soft  bottom,  a 
timber  dam  cannot  be  expected  to  last  fifty  years.  Were  this 
the  fact,  there  would  be  hardly  any  conditions  that  could  justify, 
from  a  financial  point  of  view,  the  construction  of  a  masonry 
dam.  The  present  value  of  $1000  due  fifty  years  hence  is 

at  6% $54-29 

at  4$ , $  1 40. 7 1 

at  3^ .      $228.13 

Leaving  annual  repairs  and  changes  of  value  out  of  account, 
these  figures  represent  the  excess  of  value,  per  $1000,  of  a  thing 
that  will  last  forever  over  a  thing  that  will  last  fifty  years. 
That  is  to  say,  with  the  above  reservation,  counting  interest  at 
4  per  cent,  it  would  be  as  judicious  to  spend  $85  929  for  a 
timber  dam  to  last  fifty  years  as  $  i  oo  ooo  for  a  stone  dam  to 
last  forever. 

Let  us   assume   a   masonry  dam  costing  $100000  to   last 


98  DAMS   OF  MASONRY. 

forever,  without  any  repairs.  How  would  it  compare  in  point 
of  economy  with  a  timber  dam  to  last  twenty-five  years  at  a 
first  cost  of  $60000,  and  $500  per  annum  for  repairs  ? 

1.  In  the  newly  settled  parts  of  the  country,  where  interest 
can  be  taken  at  7  per  cent:    To  put  the  second  dam  on  the 
same  footing  as  the  first,  we  must  add  to  the  first  cost  a  fund 
to  furnish  the  annual  maintenance,  and  another  fund  to  renew 
the  dam  every  twenty-five  years. 

Masonry  dam $100000 

Timber  dam,  first  cost $60  ooo 

Fund  to  yield  $500  per  annum $7  143 

"      "  renew  the  dam  every  25  years $13  552 — $80695 

Balance  in  favor  of  timber  dam $19  305 

2.  In  the  older  parts  of  the  country  where  interest  can  be 
taken  at  4  per  cent : 

Masonry  dam $100  ooo 

Timber  dam,  first  cost $60000 

Fund  to  produce  $500  per  annum $12  500 

"      "  renew  the  dam  every  25  years. .  .  .  $36014 — $108  514 

Balance  in  favor  of  masonry  dam $8514 

Compare  a  masonry  dam  to  cost  $100000  and  last  forever 
with  a  brush  dam  to  last  ten  years,  at  a  first  cost  of  $30  ooo 
and  an  annual  outlay  of  $1000  for  maintenance. 

1 .  Interest  at  7  per  cent : 

Masonry  dam $100000 

Brush  dam,  first  cost $30000 

Fund  to  produce  $1000  per  annum $14286 

$30000  every  10  years,  .  .  $31  024— $75  310 
Balance  in  favor  of  brush  dam $24690 

2.  Interest  at  4  per  cent: 

Masonry  dam $100000 

Brush  dam,  first  cost $30  ooo 

Fund  to  produce  $1000  per  annum $25  ooo 

$30000  every  10  years  .  .  .  $60250—115250 
Balance  in  favor  of  masonry  dam 2cO 


DESCRIPTION  OF  SOME  STONE  DAMS.  99 

These  computations  are  misleading  only  in  so  far  as  they 
fail  to  take  account  of  progressive  changes  in  the  rate  of 
interest  and  cost  of  work  during  the  periods  considered.  They 
serve  to  show  the  principles  on  which  such  calculations  should 
proceed.  There  are  other  considerations,  however,  in  favor  of 
permanent  dams.  The  failure  of  a  dam  usually  carries  with  it 
the  stoppage,  for  a  longer  or  shorter  period,  of  industries 
dependent  on  it,  and  entails  losses  far  in  excess  of  the  cost  of 
renewal.  Moreover,  ethical  and  aesthetic  considerations  often 
enter  into  the  question.  The  builders  of  an  important  dam 
may  desire  to  transmit  it  as  a  memorial  of  themselves  to  the 
remote  future,  and  are  sometimes  willing  to  spend  more  upon 
its  construction  than  a  close  consideration  of  pecuniary  interests 
would  require. 

Description  of  Some  Stone  Dams.— Fig.  50  is  a  section  of 
the  dam  across  the  Merrimac  River  at  Lowell,  Mass.  The 
river  here  has  a  drainage-area  of  4085  square  miles.  The 
dam  crosses  the  stream  in  an  oblique  and  irregular  line,  giving 
the  overflow  a  total  development  of  1093  feet.  In  1852  the 
water  reached  the  depth  of  13  feet  7  inches  on  this  dam.  The 
site  of  the  dam  is  a  very  firm  refractory  rock,  overlaid  by 
glacial  gravel  of  a  hardness  equal  to  some  formations  that  are 
classed  as  rock.  The  general  surface  of  the  rock  is  not  more 
than  1 6  feet  below  the  level  of  the  crest  of  the  dam;  at  the 
shores  it  rises  considerably  above  that  level.  At  one  point  a 
fissure  or  cavity  occurred  filled  with  gravel,  where  the  excava- 
tion for  the  dam  reached  to  the  depth  of  38  feet  without  finding 
rock.  A  dam  of  some  sort  has  existed  at  this  point  for  a 
century  or  more.  It  was  rebuilt  in  its  present  form,  a  part  in 
1846-7,  and  the  remainder  in  1875-6.  The  part  built  in 
1846-7  was  not  laid  in  mortar  except  the  rear  slope  and  the 
cap-stones,  so  far  as  necessary  to  exclude,  the  water.  Serious 
objections  to  this  mode  of  construction  were  developed  before 
the  remainder  of  the  work  was  commenced.  The  freezing  and 
consequent  expansion  of  the  water  in  the  cavities  of  the 
masonry  gradually  worked  out  some  of  the  stones  of  the  down- 


IOO 


DAMS  OF  MASONRY. 


stream  face.  Stones  were  noticed  projecting  6  or  8  inches 
beyond  the  face  of  the  dam.  Warned  by  this  experience,  the 
portion  subsequently  built  was  laid  in  full  mortar  except  the 
ashlar,  which  was  laid  without  mortar  and  grouted  with  pure 
Portland  cement.  This  was  done,  it  is  understood,  that  the 
stones  might  rest  in  contact  with  each  other,  and  not  be  liable 
to  derangement  in  case  of  the  subsequent  disintegration  of  the 


FIG.  50. 

mortar.  The  rubble-work  was  laid  in  mortar  of  Newark 
cement  mixed  I  to  I.  The  ashlar  work,  including  the  cap- 
stones, was  laid  to  quarter-inch  joints.  The  joints  of  the  cap- 
stones, above  the  line  AB,  were  filled  with  melted  sulphur. 
The  dowels  were  also  imbedded  in  sulphur.  The  cap-stones 
were  2  to  3  feet  wide  and  were  laid  on  an  incline,  with  the 
view  of  avoiding  any  shock  from  floating  bodies.  A  face  18 
inches  wide  was  cut  and  hammered  on  the  cap-stones  at  the 
down-stream  end  for  the  application  of  the  flashboards. 

The  writer  examined  this  dam  in  1895  after  the  new  part 


DESCRIPTION  OF  SOME  STONE  DAMS.  IOI 

had  stood  about  twenty  years.  It  was  perfectly  intact  and  had 
sustained  no  injury  of  any  kind.  The  sulphur  in  the  cap-stone 
joints  had  withstood  the  action  of  frost.  It  was  noticed  that 
both  bed  and  build  joints  of  the  face  were  largely  devoid  of 
mortar.  A  thin  stick  could  be  thrust  into  these  joints  to  a 
depth  of  1 8  inches,  and  on  withdrawing  it,  water  followed, 
bringing  disintegrated  mortar.  Mortar  used  in  rubble- work 
was  perfectly  sound  and  of  flinty  hardness.  The  only  comment 
suggested  by  this  examination  was  this :  It  appeared  to  me  that 
the  method  of  laying  the  ashlar  dry  and  grouting  the  joints  was 
not  one  to  be  copied.  The  work,  to  my  mind,  would  have 
been  better  if  the  joints  had  been  wider  and  filled  with  stiff 
mortar. 

The  total  cost  of  this  dam  is  given  as  $i  14  ooo.  This  dam 
checks  the  current  of  the  river  for  a  distance  of  about  18  miles, 
forming  a  pond  of  about  1 120  acres. 

Fig.  51  is  a  section  of  the  Essex  Company's  dam  across 
the  Merrimac  River  at  Lawrence,  where  the  stream  has  a 
drainage-area  of  4600  square  miles.  In  describing  this  work 
we  cannot  do  better  than  adopt  the  exact  language  of  the 
Tenth  Census  Report:* 

' '  The  development  of  the  water-power  at  this  place  dates 
from  the  year  1845,  when  the  owners  of  the  land  and  water- 
power  were  incorporated  as  the  Essex  Company  with  a  capital 
of  $i  ooo  ooo.  Steps  were  at  once  taken  toward  the  utilization 
of  the  power,  and  on  July  5,  1845,  the  contract  was  concluded 
for  the  building  of  the  substantial  dam  which  holds  back  the 
waters  of  the  river  and  diverts  them  into  the  channels  of 
industry.  The  structure  is  built  in  a  curve,  the  chord  being 
900  feet,  and  the  centre  ordinate  14.97  feet.  Its  maximum 
height  is  40^  feet,  and  its  average  height  about  32  feet,  the 
breadth  at  the  base  being  about  35  feet.  The  front  face  has  a 
ba'tter  of  I  in  12;  the  top  or  capping  is  level  for  3  feet  from  the 
face,  then  slopes  back  or  up-stream  i  foot  in  3  feet  for  12  feet, 

*  Tenth  U.  S.  Census  Report,  vol.  XVI.     Water-power  of  Eastern  New 
England,  p.  25. 


102  DAMS  OF  MASONRY. 

beyond  which  the  back  is  stepped  off  at  a  slope  of  45°.  Its 
section  is  shown  in  Fig.  51.  It  is  composed  entirely  of  solid 
stone  masonry  resting  on  a  rock  foundation,  which  is  stepped 
off  to  receive  it,  the  front  of  the  dam  being  secured  by  blasting 
out  a  trench  in  the  rock  .along  the  entire  length,  in  which  the 
first  course  of  granite  masonry  is  laid,  all  the  stones  being 


FIG.  51. 

headers  and  the  next  course  above  being  all  stretchers  dowelled 
to  the  foundation-course.  The  face  of  the  dam  is  all  of  dressed 
stone,  the  headers  and  stretchers  of  each  course  being  dove- 
tailed together,  and  the  capping-stones  being  dowelled  to  each 
other  and  to  the  next  facing-course  below.  The  remainder  of 
the  dam  is  of  rough  stone  laid  in  cement,  with  a  back-filling 
of  earth  sloping  6  to  i .  The  level  of  the  water  may  be  raised 
3  feet  above  the  crest  of  the  dam  by  means  of  flashboards,  in 
lengths  of  16  feet,  resting  against  i^-inch  iron  bolts  inserted 


DESCRIPTION   OF  SOME   STONE   DAMS.  10$ 

at  intervals  of  20  inches  in  holes  drilled  in  the  capping-stones. 
The  top  of  the  dam  is  34. 12  feet  on  the  company's  scale.  At 
the  south  end  of  the  dam  is  a  substantial  wooden  fishway. 
The  excavation  for  the  dam  was  begun  August  I,  1845,  the 
first  stone  laid  September  19  of  the  same  year,  and  the  struc- 
ture completed  in  1848,  its  construction  having  occupied  almost 
exactly  three  years.  The  rock  excavation  in  preparing  the 
foundation  amounted  to  1700  cubic  yards;  the  quantity  of 
masonry  laid  in  cement  was  29000  cubic  yards.  The  surface 
of  hammered  granite  was  148  ooo  square  feet.  The  cost  of  the 
dam,  including  coffer-dam  and  all  incidentals,  was  $250000. 
The  agent  and  engineer  of  the  Essex  Company  was  Charles 
S.  Storrow,  who  designed  the  dam  and  canals  and  the  general 
development  of  the  water-power,  and  he  was  efficiently  aided 
in  carrying  out  the  work  after  April,  1846,  till  its  completion, 
by  Captain  Charles  H.  Bigelow,  as  engineer  in  charge  of  con- 
struction. 

"The  dam  crosses  the  stream  in  an  oblique  direction,  and 
on  each  side  there  are  extensive  wing  walls,  that  on  the  south 
side  being  324  feet  long,  and  that  on  the  north  side  405  feet, 
making  with  the  overfall  a  total  length  of  1629  feet.  There 
is  a  canal  on  each  side  of  the  river.  That  on  the  north  side, 
which  is  the  principal  one,  is  5330  feet  long,  100  feet  wide  at 
the  upper  end,  and  60  at  the  lower  end,"  etc.,  etc.  We  shall 
have  occasion  to  refer  to  these  canals  later. 

This  dam  has  now  stood  full  fifty  years,  meeting  in  all 
respects  the  expectations  of  its  builders.  It  is  not  understood 
to  have  suffered  any  material  damage  from  any  cause  during 
that  time.  The  profile  of  the  dam  makes  it  abundantly 
massive.  Suitable  calculations  would  show  that  it  derives  no 
additional  stability  from  its  curved  outline. 

It  is  not  easy  to  see  what  rational  purpose  is  served  by  the 
bank  of  earth  on  the  up-stream  side.  The  whole  work  being 
laid  in  cement  mortar,  it  cannot  be  presumed  that  any  necessity 
existed  for  this  deposit  for  the  prevention  of  leakage,  while 
there  can  be  no  doubt  that  it  increases  the  static  pressure  tend- 


IO4  DAMS  OF  MASONRY. 

ing  to  overturn  the  dam.  In  any  stage  of  the  water  such  that 
injury  from  floating  bodies  is  to  be  apprehended,  this  arrange- 
ment tends  to  increase  the  risk  of  such  injury  by  increasing  the 
velocity  with  which  such  bodies  approach  the  dam,  and  the 
consequent  shock  with  which  they  strike  it. 

As  may  be  gathered  from  the  foregoing,  the  spillway  of  this 
dam  is  900  feet  long,  while  that  of  the  Lowell  dam  is  longer 
by  nearly  200  feet.  In  the  great  flood  of  1852  the  water  is 
recorded  a!s  having  stood  10  feet  deep  on  the  former,  and  13 
feet  7  inches  on  the  latter.  This  seeming  anomaly  is  probably 
explainable  in  this  manner:  The  Lowell  dam  is  nowhere  more 
than  1 6  feet  above  the  bed  of  the  stream,  and  at  that  time  was 
comparatively  lower  than  at  present,  the  rock  being  covered 
with  its  deposit  of  gravel,  protected  by  a  pitching  of  heavy 
stone.  The  dam  during  the  flood  was  "drowned,"  the  water 
being  but  a  few  feet  higher  above  than  below.  Moreover,  a 
considerable  stretch  of  the  Lowell  dam  runs  parallel  with  the 
.current  and,  in  such  a  stage  of  the  river,  counts  for  little  as 
regards  the  discharge.  The  Lawrence  dam,  on  the  contrary, 
is  substantially  straight,  nearly  square  with  the  current,  and 
too  high  to  be  drowned. 

Fig.  52  is  a  section  of  the  dam  constructed  in  1890-93 
across  the  Colorado  River  at  Austin,  Texas,  designed  and 
partly  executed  under  direction  of  the  author.  The  river  at 
this  point  has  a  drainage-area  of  32  ooo  square  miles  according 
to  the  most  reliable  maps.  It  is  a  typical  Southern  stream, 
the  ordinary  low-water  volume  running  from  600  to  1000  cubic 
feet  per  second,  and  this  appears  to  be  sustained  wholly  by 
springs* issuing  from  the -rock.  A  simultaneous  rise  of  all  the 
tributaries  is  very  rare,  but  when  this  occurs  it  results  in  an 
enormous  flood.  A  flood  is  said  to  have  occurred  in  1869 
which  raised  the  water  45  feet  at  Austin,  and  brought  down 
such  a  volume  o/  drift  as  to  form  a  permanent  raft  farther  down 
the  stream,  which  remained  in  place  many  years.  The  flow 
at  that  time  must  have  been  200000,  possibly  250000,  cubic 
feet  per  second.  Floods  approach  with  such  rapidity  as  to 


DESCRIPTION   OF  SOME   STONE  DAMS. 


I05 


jeopardize  the  lives  of  people  who  are  fording  the  stream. 
After  the  crisis  of  the  flood  is  past  it  rapidly  subsides,  and  in  a 
few  days  the  river  reverts  to  its  normal  condition,  except  that 
the  water  remains  turbid  for  a  long  time.  The  water  falls  a 
little  lower  in  summer  than  in  winter,  but  there  is  no  distinctly 
high-water  season.  The  aggregate  flow  of  the  stream  prob- 


FIG.  52. 

ably  does  not  amount  to  a  tenth  part  pf  what  is  to  be  expected 
from  an  equal  drainage-area  in  Northern  latitudes. 

The  river  here  flows  in  a  formation  of  shelly  lime  rock  lying 
in  nearly  horizontal  strata.  It  has  worn  a  canyon  45  or  50 
feet  deep  and  some  1200  feet  wide,  about  half  this  width  being 
filled  with  argillaceous  deposit  brought  down  by  the  stream. 
The  dam  raises  the  water  60  feet  above  the  low-water  stage 
and  has  an  overflow  about  1140  feet  long.  It  forms  a  lake 


106  DAMS   OF  MASONRY. 

extending  some  20  miles.  Although  the  question  of  the 
abrasion  of  the  bottom  was  here  of  subordinate  importance  by 
reason  of  the  small  flow,  the  base  of  the  dam  was  spread  out 
into  a  broad  apron  or  toe  to  shield  the  rock  from  the  direct 
impact  of  the  stream.  It  was  contemplated  by  the  engineer 
to  extend  this  apron  by  a  bed  of  concrete  if  found  necessary. 
A  flood  such  as  occurred  in  1869  would  probably  raise  the 
water  15  feet  on  the  crest  of  the  dam,  but  in  such  a  flood  the 
water  would  be  45  feet  deep  on  the  down-stream  side,  and  the 
action  on  the  bottom  would  be  probably  less  severe  than  in  a 
lower  stage. 

The  original  design  of  the  dam  did  not  contemplate  a 
rounded  outline  at  the  top,  but  a  crest  formed  as  indicated  by 
the  dotted  lines.  The  expectation  was  that  it  might  in  future 
become  desirable,  for  the  more  economical  use  of  the  water, 
to  use  flashboards  6  or  8  feet  high  to  be  thrown  down  on  the 
approach  of  floods.  The  rounded  outline  was  substituted  by 
the  board  controlling  the  work.  The  faces  of  the  dam  were 
laid  in  granite  which  occurs  of  good  quality  and  in  inexhausti- 
ble quantity  at  Burnet,  some  75  or  80  miles  up  the  river.  The 
up-stream  face  was  laid  in  courses  36  inches  thick,  the  joints 
being  pointed  with  pure  cement.  At  the  toe  of  the  dam  very 
heavy  stones  were  used,  some  weighing  as  much  as  6  tons. 
Dowells  and  cramps  were  also  inserted  at  this  point.  The 
interior  of  the  work  was  laid  with  such  stone  as  could  be  found 
in  the  vicinity.  The  entire  work  was  laid  in  Portland  cement 
supposed  to  be  mixed  3  to  i.  A  cable  with  a  clear  span  of 
1350  feet  was  used  in  the  construction  of  this  work.  The 
entire  dam  contains  some  90  ooo  cubic  yards  of  masonry  and 
cost  a  little  over  $600000.  This  work  is  described  in  the 
technical  journals,  especially  the  Engineering  News* 

Flgs-  53.  54,  54*.  and  54^  represent  the  dam  now  in 
course  of  construction  and  nearly  complete  (January,  1899),  at 
Holyoke,  Mass.,  to  replace  the  wooden  dam  already  described. 

*  Entering  New*.  N.  Y.,  vol.  xxix,  p/Sy;  al«o  numerous  article,  ia 

succeeding  volumes  up  to  the  period  of  its  destruction  in  April,  1900. 


DESCRIPTION   OF  SOME   STONE   DAMS. 


TO/ 


Fig.  540  shows  the  position  of  the  new  dam  with  reference  to 
the  existing  wooden  dam.  It  will  be  noticed  that  the  toe  is  so 
formed  as  to  give  an  upward  direction  to  the  escaping  water. 
The  facing  of  the  dam,  both  up-  and  down-stream,  is  to  be  of 
granite.  The  specifications  require  the  level  crest  of  the  dam, 


FIG.  S3- 

and  the  face  for  3  feet  below  the  same,  to  be  fine-hammered. 
In  the  down-stream  face  masonry  all  contact  surfaces  are  to  be 
cut  to  lay  a  quarter-inch  joint.  The  up-stream  face  is  to  be  of 
split  granite  cut  to  half-inch  joints.  The  interior  is  to  be  of 
rubble  composed  of  stone  found  in  the  vicinity  of  the  dam. 

The  writer  sees  no  reason  to  doubt, that  a  safe  and  perma- 
nent dam  can  be  built  in  accordance  with  this  design.  He 
will,  however,  offer  a  few  comments  upon  some  of  its  features. 

i .  The  masonry  of  the  toe  appears  to  be  sunk  in  the 
natural  rock,  and  the  stones  which  stand  on  edge  or  on  end 
appear  to  derive  their  stability  from  their  backing  of  natural 
rock.  This  arrangement  appears  to  assume  what  cannot  be 
realized.  The  toe-stones  necessarily  lie  all  at  the  same  level. 


io8 


DAMS  OF  MASONRY. 


DESCRIPTION  OF  SOME  STONE  DAMS.  IOQ 

The  bed-rock  cannot  be  assumed  to  lie  at  a  uniform  level.  Its 
contour  cannot  be  known  till  coffer-dams  are  built  and  the 
work  is  commenced.  It  will  at  some  points  lie  at  or  below  the 
bottom  of  the  outer  toe-stone.  In  such  a  situation  it  would 
apparently  be  necessary  to  introduce  a  supplementary  mass  of 
masonry.  The  disposition  adopted  at  the  toe  of  the  Austin 
dam  appears  preferable  as  being  more  conformable  to  the 
actual  shape  of  the  bottom. 

2.  I  am  not  able  to  perceive  any  advantage  in  the  upward 
turn  at  the  extremity  of  the  apron.  It  does  not  diminish  the 
velocity  with  which  the  water  leaves  the  dam,  the  commotion 
wnich  it  undergoes  in  coming  to  rest,  or  its  consequent  wear 
and  abrasion  of  the  bottom.  The  water  after  leaving  the  dam 
comes  to  rest  by  a  series  of  whirling  movements.  The  violence 
and  amplitude  of  these  movements  depend  upon  the  initial 
velocity  of  the  water,  not  at  all  upon  its  initial  direction.  On 
the  other  hand,  the  disadvantages  of  this  feature  are  obvious. 
Heavy  bodies  coming  over  the  dam  are  acted  on  by  centrifugal 
force,  which  tends  to  separate  them  from  the  convex  face,  and 
to  hold  them  more  firmly  against  the  concave  face.  On 
reaching  the  lowest  point  of  their  journey,  if  the  remainder  of 
the  dam  runs  level,  they  simply  press  upon  it  with  their  weight, 
if  not  immersed,  and  if  immersed,  exert  no  pressure  on  it. 
The  upward  turn  of  the  masonry  brings  them  into  strong  con- 
tact with  it,  and  gives  them  a  frictional  hold,  tending  to 
separate  the  last  stone  from  the  rest.  Should  the  backing  fail 
or  wear  out,  the  outer  stone  would  be  very  likely  to  separate, 
and  a  slight  separation  would  greatly  increase  the  violence  of 
the  shocks.  Against  this  action  the  dowels  represented  in  the 
drawing  have  little  effect. 

3.  Nothing  can  be  more  fanciful  than  any  attempt  to  con- 
form the  face  of  the  dam  to  any  law  of  movement  of  the  water, 
as,'  for  instance,  to  give  it  the  form  of  the  trajectory  of  a  pro- 
jectile. This  necessarily  involves  an  assumption  as  to  the 
velocity  of  the  water.  If  the  curve  is  correct  for  that  assumed 
velocity,  it  is  incorrect  for  all  others.  The  only  object  of  the 


1 10  DAMS   OF  MASONRY. 

curve  is  to  shield  the  bottom  from  the  direct  impact  of  the 
water.  It  is  just  as  well  to  secure  this  result  by  arcs  of  circles  as 
to  waste  time  in  conforming  the  work  to  a.more  complex  curve. 

4.  It  is  a  mistake  to  suppose  that  a  curved  face  will  secure 
this  work  against  the  shock  of  floating  bodies.      In  high  stages 
of  water,  where  there  is  a  depth  of  8  feet  or  more  on  the  toe 
of  the  apron,  a  reverse  current  will  be  set  up  which  will  cause 
bodies  to  strike  the  curved  face  with  considerable  force. 

5.  No  part  of  the  dam   is  so  free  from  liability  to  injury  as 
the  crown,  and  no  part  stands  less  in  need  of  extraordinary 
reinforcement.     Water  and  floating  bodies  approach  this  part 
with  very  low  velocity.      The  velocity  becomes  rapid  only  in 
high   water  when   the   crown   stands   in   no   danger   of  being 
touched  by  floating  bodies.      At  this  point  water  and  floating 
bodies  have  no  power  for  mischief.      This  power  is  acquired  in 
going  over  the  dam.      It  is  in  the  lower  part  of  the  work  that 
strength  and  solidity  are  required.      In  the  light  of  these  prin- 
ciples it  is  not  easy  to  see  the  necessity  for  the  great  precautions 
against  injury  to  the  crown  of  the  dam.      The  steps  or  offsets 
on  the  up-stream  face  of  the  dam  were  designed  for  conven- 
ience in  controlling  the  water  during  construction.      At  least 
they  are  said  to  have  served  that  purpose.      The  existing  dam 
serves  as  a  coffer-dam  to  exclude  the  water  from  the  work  in 
progress.      In  low  stages  the  flow  of  the  stream  can  be  turned 
through  the  water-power  canals,  and  either  drawn  by  the  mills 
or  allowed  to  go  to  waste.      The  old  dam,  however,  admits  a 
large  amount  of  leakage  which  has  to  pass  the   dam   under 
construction.     This  leakage  goes  through  a  gap  in  the  stone 
dam,  till  it  becomes  necessary  to  raise  the  masonry.      Then 
the  gap  is  closed  by  a  coffer-dam,  and  the  water  is  raised  and 
turned  through  a  second  gap.     The  steps  afford  a  convenient 
footing  for  these  coffer-dams. 

Fig.  55*  is  a  section  of  the  dam  recently  constructed  by  the 
Hudson  River  Power-transmission  Company  across  the  Hudson 
at  Mechanicsville,  N.  Y.  At  this  point  the  river  has  a  drain- 

*  Engineering  JVews,  N.  Y.,  vol.  XL.  p.  130. 


DESCRIPl^ION   OF  SOME  STONE   DAMS. 


Ill 


age-area  of  about  4500  square,  miles.-  An  island  separates  the 
river  into  two  channels,  the  easterly  of  which  is  occupied  by 
the  spillway  with  a  length  of  800  feet.  The  westerly  channel 


Section  of  Main    Concrete    Dam    She  wina 
Overfall  and  Section  of  Abutment. 

FIG.   55- 

is  closed  to  the  free  passage  of  water,  by  the  power-house  in 
connection  with  a  dam  rising  above  the  level  of  high  water, 
and  provided  with  waste-gates  for  emergencies.  Waste-gates 
are  also  inserted  in  one  of  the  abutments  of  the  main  dam, 
i.e.,  the  spillway.  There  are  sixteen  of  these  waste-gates  in 
all,  each  4  feet  wide  and  6  or  7  feet  high.  The  figure  shows 
the  spillway  in  section,  and  the  abutments  in  elevation.  The 
rock  at  this  point  is  of  a  somewhat  friable  character,  and,  as 
will  be  noticed,  the  spillway  has  a  curved  outline,  the  toe  or 
apron  being  so  formed  as  to  give  a  slight  upward  direction  to 
the  escaping  water.  It  extends  to  some  distance  beyond  the 
tangent  point  of  the  curve  in  a  straight  line.  This  is  preferable 
to  the  form  of  the  Holyoke  dam,  as  the  centrifugal  force  ceases 
to  act  at  the  tangent  point  of  the  curve.  This  work  is  specially 
interesting  for  the  reason  that  the  dams,  abutments,  and  power- 
house foundations  are  composed  wholly  of  concrete.  It  will  be 
interesting  to  observe  how  this  material  stands  the  wear  of 


112 


DAMS  OF  MASONRY. 


water  and  ice  on  the  curved  part.      Fig.  56  is  a  photographic 
view  of  the  spillway  in  the  easterly  channel  with  water  coming 


FIG.  56. 


FIG.  57- 

over,  and  Fig.  57  is  a  view  of  the  power-house  occupying  the 
westerly  channel,  from  the  up-stream  side. 

A  Dam  and  Bridge  Combined. — There  is  nothing  incon- 
gruous in  the  idea  of  combining  a  bridge  with  a  dam,  the 
roadway  resting  on  the  abutments  and,  if  necessary,  on  piers 
springing  from  the  dam  and  apron.  Such  structures  are  not 
so  common  as  might  be  expected  considering  the  obvious 
advantages  of  the  arrangement,  especially  where  flashboards 
are  used,  the  bridge  offering  a  safe  and  convenient  mode  of 


A    DAM  AND    BRIDGE    COMBINED. 


FIG.  58. 


114 


DAMS   OF  MASONRY. 


handling  the  latter.      Figs.  58  and  59*  show  a  construction  of 
this  kind  erected  on  the  Blackstone  River  at  Lonsdale,  R.  I., 


FIG.  s8«. 


••"  •_    '  "  '-—•  •'•' 


FIG.  59. 


in   1893-4,   by  the  Lonsdale  Company,  which  has  extensive 
cotton-mills  at  this  point,  the  bridge  forming  a  communication 

*  Engineering  News,  N.  Y..  vol.  xxxin.  p.  166. 


A    DAM  AND   BRIDGE    COMBINED.  11$ 

between  mills  on  opposite  sides  of  the  river.  Fig.  58  shows 
the  work  in  plan,  and  Fig.  59  in  section.  Fig.  58^:  is  a 
down-stream  view  of  east  half  of  dam  with  gate-chamber. 
The  dam  raises  a  head  of  12  or  14  feet.  It  consists  of  a  spill- 
way of  rubble  masonry,  faced  with  granite  ashlar,  furnished 
with  a  massive  apron.  Five  piers  each  5  feet  in  thickness  rest 
partly  on  the  apron  and  partly  on  the  dam,  and  sustain  a 
single-track  railroad  suited  to  the  heaviest  locomotives, 
together  with  a  footway.  The  bridge  floor  is  about  8  feet 
above  the  crest  of  the  dam.  Uprights  reach  from  the  crest  of 
the  dam  to  the  floor  of  the  footway  to  sustain  the  flashboards, 
and  the  footway  carries  hand-gearing  whereby  the  latter  are 
removed  and  put  in  place.  Topographical  considerations 
require  a  curve  in  this  part  of  the  track,  which  is  the  reason  for 
the  curved  outline  of  the  bridge.  The  Blackstone,  at  this 
point,  has  a  drainage-area  of  some  43  5  square  miles. 


CHAPTER   V. 
APPENDAGES   OF   DAMS. 

Flashboards. — The  height  of  a  water-power  dam  is  usually 
limited  by  agreement  with  millowners  above,  by  decree  of 
court,  by  legislative  grant,  or  by  some  other  condition  beyond 
the  control  of  the  owners.  It  is  usually  subject  to  the  condi- 
tion of  doing  no  injury  to  the  next  dam  above,  even  in  a  stage 
of  high  water;  a  condition  which  necessitates  the  wasting  ot 
some  fall  between  the  consecutive  dams  in  seasons  of  low 
water.  During  high  stages  the  water  will  rise  to  a  greater  or 
less  height  on  the  spillway,  depending  on  the  length  of  the 
same,  and  the  extent  of  drainage-ground  above.  Without 
considering  such  floods  as  occur  at  intervals  of  a  generation  or 
more,  there  is  a  stage  which  maybe  called  "ordinary  flood 
height,"  i.e.,  such  floods  as  maybe  expected  once  or  twice 
every  year.  Below  this  level  the  banks  and  shores  of  the 
stream  are  of  no  value.  No  crops  can  be  produced,  no  fences 
or  buildings  can  be  placed,  no  material  injury  can  accrue  to 
any  interest  by  the  permanent  maintenance  of  the  water  at 
this  level,  provided  the  barriers  be  removed  and  free  passage 
given  to  the  water,  in  time  of  flood.  These  conditions  give  rise 
to  the  use  of  flashboards. 

The  right  to  maintain  flashboards  can  usually  be  obtained 
readily  from  riparian  proprietors,  and  is  of  great  value  to  the 
owner  of  the  dam,  not  only  increasing  his  available  head  in 
low  stages  of  the  stream,  but  enabling  him  to  hold  to  a  larger 
extent  the  flow  of  nights  and  Sundays  for  use  in  working 
hours.  This  privilege,  however,  is  always  granted  under  the 
expressed. or  implied  agreement  that  the  passage  of  water  over 

116 


FLASHBOARDS. 


117 


the  weir  shall  be  left  free  during  high  stages  of  the  stream, 
otherwise  the  privilege  of  applying  flashboards  would  simply 
amount  to  the  privilege  of  raising  the  dam  so  many  feet  higher. 
The  fulfilment  of  this  obligation  requires  a  form  of  flashboard 
barriers  susceptible  of  ready  removal  without  reference  to  the 
stage  of  the  stream,  a  condition  but  imperfectly  fulfilled  by  the 
method  in  common  use,  which  consists  generally  of  boards 
resting  against  iron  pins  let  into  the  dam  as  shown  in  Fig.  60. 
This  figure  represents  a  system  of  flashboards  4  feet  high,  which 
is  the  greatest  height  ever  attempted  by  this  method  so  far  as 
the  author  is  aware,  heights  of  2  feet  being  most  common. 


FIG.  60.  FIG  61. 

This  arrangement  holds  the  water  well  enough ;  but  if 
caught  in  a  flood,  there  is  no  relief  till  the  pins  are  broken 
down  or  bent  over  by  the  pressure  of  the  water  or  by  ice  or 
drift,  in  which  event  the  boards  go  down-stream.  When  the 
boards  are  up,  with  no  water  behind  them,  as  often  happens, 
they  are  liable  to  fall  off  or  be  blown  off  by  the  wind  if  not 
fastened  to  the  pins.  Fig.  61  shows  one  mode  of  fastening 
them,  viz.,  by  small  staples  driven  into  the  boards  and  embrac- 
ing the  pins.  Rough  unplaned  boards  are  used  either  butted 
together  or  overlapping  at  the  ends.  The  joints  are  tightened 
by  throwing  in  horse-dung,  sawdust  mixed  with  sand,  or  similar 
material. 

At  most  water-powers,  notice  of  the  approach  of  a  flood 
may  be  given  in  time  to  allow  of  the  removal  of  the  flashboards 
and  pins,  especially  if  a  trained  crew  of  men  are  kept  for  that 
purpose.  Otherwise  the  only  guaranty  of  a  clear  waterway  for 
the  flood  is  the  bending  down  of  the  pins.  For  this  reason, 


Il8  APPENDAGES  OF  DAMS. 

the  diameter  and  number  of  the  pins  should  be  such  as  to  hold 
the  water  with  safety  up  to  the  top  of  the  flashboards,  and  to   * 
yield   when   the  water    rises    much   above  that    height.*     To 
determine  the  proper  size  and  spacing  of  the  pins,  we  must 
consider  the  mechanical  principles  of  the  case. 

Let  h2  represent  the  height  of  water  above  the  crest  of  the 
dam;  //:  represent  the  height  of  water  above  the  top  of  flash- 
boards.  The  height  of  the  centre  of  pressure  of  the  flashboards 
above  the  crest  of  the  dam  is 


When  the  water  is  at  the  top  of  the  flashboards,  /it  =  o,  //.,  = 
height  of  flashboards,  and  //=//,—  |//2  =  £  height  of  flash- 
boards. 

The  total  pressure  on  the  flashboards  to  be  borne  by  a  pin 
will  be,  if  /represent  the  space  between  two  consecutive  pins, 

P  =  $62.  5  /(//2a  —  //,*). 

The  bending  moment  on  a  pin  therefore  will  be  HP  =  i  x 
62-5/(/r22  —  //i2)//.  This  is  the  external  bending  moment.  It 
is  met  by  the  internal  bending  moment  of  resistance,  in  = 

—  /</',  in  which  /=  the  maximum  strain  on  the  fibres  in  pounds 

per  square  inch,  and  d  —  the  diameter  of  the  pin  in  inches. 

Suppose  flashboards  2  feet  high  held  by  i-inch  pins  2  feet 
apart.      The  pressure  against  a  pin  with  water  at  top  of  flash- 

*  The  total  pressure  on  the  flashboards  appertinent  to  one  pin  is 
62.5/(A.  -  *.)**  +2  7"  =  J  X  62.5  W  -  *,*)  =  P.  The  pressure  on  an  element 
dh  of  the  flashboards  is  62.5//W7*.  Its  moment  with  reference  to  the  surface 

is   62.5//4V/4.     Total   moment  =  62.5;   /    *  tfdh  =  62.5/(/J23  —  /,,3)£.     Let  X 

t/!*j 

represent  the  depth  of  the  centre  of  pressure,  then  PX=  total  moment,  or 
62.5/(//2s  —  A,3)  2        zhj-hj  ih*  —  h* 

*m*  whence  H-^-~- 


FLASHBOARDS.  119 

boards  is  £  X  62.5  X  2  X  4  —  250  pounds.  The  external 
moment  is  12  X  i^2  X  250  =  2000  inch-pounds.  The  internal 

moment  is  — f;  say  -faf.      .•./"  =  10  X  2000  =20  ooo  pounds 

— a  strain  which  would  be  admissible  under  the  circumstances. 

Suppose  the  water  to  rise  2  feet  above  top  of  flashboards. 

Jit  =  4,  //j  —  2.      Pressure  on  a  pin  =  %  X  62.5  X  2  X  12  = 

2  64—  8 
750  pounds.     //=  4  — g— -  -  =  0.8889  feet  =  I0f  inches. 

External  moment  =  750  X  iof  =  8000.     .  •.  —  f—  8000,  and 

f  =  80000  nearly.  As  ordinary  iron  does  not  possess  this 
strength,  the  pins  would  break  down  before  the  water  had  risen 
2  feet  above  the  top  of  the  flashboards. 

Again,  consider  4-foot  flashboards  held  by  i^-inch  pins 
I  foot  apart.  h2  =  4,  Jil  =  o.  Pressure  =  £  X  62.5  X4X 

4  =  500.     H  —  1 6  inches;    moment  —  8000..     .  -.  —  X/X 

3.375  =  8000,  and  f  —  say  10  X  8000  -f-  3.375  —  23  700. 
For  the  purpose  in  view  there  would  be  little  risk  in  subjecting 
iron  to  this  strain.  When  the  water  rises  2  feet  above  the 
flashboards  h.2  —  6,  /^  =  2,  P  —  £  X  62.5  X  -32  =  1000. 

H  —  6 7 =  1.6667    feet  =  20    inches.       External 

3  36-4 

moment  =  20  ooo  inch-pounds.    Internal  moment  =  — f  X  3f  • 

32 

32          20  OOO  20000 

*  x  "3^75" =  say  I0  x  3^375" =  nearly6oooolbs- 

This  result  shows  that  while  pins  of  ordinary  iron  would 
stand  safely  with  water  at  top  of  flashboards,  they  would  fail 
before  the  water  had  risen  much  over  2  feet  above  the  top. 
Where  a  height  of  4  feet  is  attempted  the  pins  are  often  of 
different  lengths,  alternately  2  and  4  feet  as  at  Fig.  -61. 

For  regulating  the  height  of  water  at  waste  ways  in  canals 
which  are  not  subject  to  river  fluctuations  the  form  of  flash- 
boards  indicated  at  Figs.  62  and  63  is  often  used.  These 


120 


APPENDAGES   OF  DAMS. 


consist  of  stout  boards,  4  to  6  feet  in  length,  placed  horizontally 
and  provided  with  handles.  Piers  are  erected  on  the  weir,  built 
of  plank  6  or  8  inches  thick,  set  edgewise  one  above  the  other, 


FIG.  62. 


FIG.  63. 

and  confined  by  long  bolts  anchored  in  the  dam.      The  piers 
sustain  planks,  forming  a  foot-bridge  for  the  use  of  attendants 
The  interval  between  the  handles  of  the  boards  is  narrowest 
for  the  upper  ones  and  wider  for  the  lower.      In  front  of  the 


FLA  SHBOA  RD  S.  121 

boards  is  a  rest  for  the  workman's  foot,  otherwise  he  could  not 
exert  his  full  strength  in  lifting  the  boards  against  the  friction 
incident  to  the  pressure  of  the  water.  When  he  lifts  a  board 
he  passes  it  under  his  feet,  stepping  between  the  handles,  and 
leans  it  against  the  railing  in  rear,  so  that  the  boards  are 
always  in  the  order  required  to  go  upon  the  dam. 

This  plan  of  wasteway  would  not  ordinarily  serve  for  a 
natural  stream,  as  the  flood  conditions  would  require  the  foot- 
bridge to  be  placed  too  high  for  convenience  of  handling  the 
boards.  A  dam  provided  with  flashboards  of  substantially  this 
form  has,  however,  existed  at  Hyde  Park  on  the  Neponset 
River  for  many  years  and  has  worked  satisfactorily.  The 
Neponset  flows  from  extensive  meadows  and  is  not  liable  to 
great  freshets.  The  owners  of  the  dam  are  obliged  to  limit  the 
height  of  water  to  avoid  injury  to  meadow-owners  above.  The 
combination  of  a  highway  or  railroad  bridge  with  a  dam,  as 
adopted  at  Lonsdale,  R.  I.,  Figs.  58  and  59,  admits  the  use 
of  mechanical  tackle  for  handling  flashboards  and  is  susceptible 
of  more  extended  application  than  it  has  yet  received. 

The  removal  of  a  system  of  flashboards  sustained  by  pins, 
on  the  approach  of  a  flood,  is  not  always  possible.  The 
ordinary  operation  of  such  a  dam,  in  low  water,  is  this:  The 
water  is  usually  found  at  the  top  of  the  flashboards  in  the 
morning,  giving  a  reserve  of  water  in  the  pond.  During  the 
day  the  water  is  drawn  from  the  pond  faster  than  it  enters,  and 
gradually  falls.  Late  in  the  day  it  becomes  safe  for  men  to  go 
upon  the  dam  to  remove  the  boards.  If  at  that  time  it  is 
known  that  the  water  will  be  high  on  the  following  day,  the 
boards  may  be  removed.  If  heavy  rains  occur  during  the  night 
while  the  flashboards  are  up,  the  water  may  not  fall  during  the 
ensuing  day  sufficiently  to  permit  their  removal,  and,  the  river 
continuing  to  rise,  they  must  go  down-stream. 

Many  water-power  streams  are  subject  to  ordinary  floods 
of  6  feet  and  more,  and  no  material  injury  to  any  riparian 
interest  would  result  from  the  maintenance  of  flashboards  of 
that  height  provided  free  way  could  be  given  in  time  of  flood. 


122  APPENDAGES   OF  DAMS, 

The  maintenance  of  this  height  by  the  method  of  pins  would 
probably  be  impossible,  and,  if  possible,  the  loss  of  the  flash- 
boards  at  every  freshet  would  be  a  serious  matter.  Fig.  64  is 
a  design  for  a  system  of  flashboards  to  maintain  this  .height, 
and,  at  the  same  time,  to  admit  of  being  lowered  in  any  stage, 
of  the  river  without  danger  to  the  workmen.  This  is  given  as 
a  suggestion  worthy  of  study,  not  as  a  device  sanctioned  by 
experience  and  usage.  Fig.  64  shows  the  method  as  applied 


FIG.  "64. 

to  an  existing  dam.  Its  application  to  a  dam  specially 
designed  with  that  view  would  be  simpler.  The  barrier  con- 
sists of  a  line  of  shutters  hinged  to  the  up-stream  crest  of  the 
dam  and  supported  when  up  by  props  resting  near  the  down- 
stream crest.  When  down,  the  shutters  lie  flat  on  the  dam  and 
are  very  little  exposed  to  injury.  When  the  shutters  are  up, 
a  chain  is  stretched  along  the  top  of  the  dam  between  the  props 
and  shutters,  and  runs  from  the  abutment  to  a  capstan  located 
down-stream  on  the  bank,  Fig.  64^.  By  winding  in  on  the 
capstan,  any  desired  strain  can  be  brought  upon  the  outside 
prop.  When  this  yields  the  strain  comes  on  the  next  prop 
and  the  shutters  can  then  be  thrown  down  in  succession.  Fig. 
640  shows  the  situation  in  plan.  It  shows  the  arrangement 
that  would  be  proper  in  case  of  an  angle  in  the  dam,  as  some- 


FLASHBOARDS. 


123 


times  occurs.  A  trapezoidal  pier  would  be  built  up,  forming- 
an  abutment  for  the  shutters  to  close  against.  The  prop  at 
the  angle  would  be  under  a  considerable  strain  from  the  tension 
on  the  chain,  but  not  so  great  as  the  exterior  prop,  and  the 
latter  would  yield  first.  After  the  shutters  have  been  thrown 
down  by  reason  of  high  water,  they  are  not  required  to  be 


X 


FIG.  64^. 


raised  again  till  the  stream  has  fallen  to  a  stage  allowing  the 
entire  flow,  at  certain  hours,  to  be  drawn  by  the  mills.  At 
such  a  time  the  water  is  below  the  cap  of  the  dam,  and  the  rais- 
ing of  the  shutters  and  adjustment  of  the  chain  is  perfectly 
simple.  When  the  water-pressure  is  off  the  shutters  they 
might  be  liable  to  the  same  difficulty  as  is  met  with  in  the  case 
of  flashboards  supported  against  pins,  viz.,  being  lifted  off  the 
props  by  the  pressure  of  the  wind  and  allowing  the  latter  to 
fall.  This  would  be  obviated  by  employing  the  form  of  hinge 
shown  at  Figs.  64$  and  64^,  which  limits  the  movement  of  the 
shutter,  and  allows  it  to  be  strained  up  with  considerable  force 
before  inserting  the  prop.  The  fall  of  the  shutter  is  cushioned 
by  the  body  of  water  beneath  it,  which  can  never  fail  to  be 
present  when  the  necessity  arises  for  throwing  down  the 
barrier.  When  lying  flat  on  the  masonry  the  shutter  can  re- 
ceive no  injury  from  floating  bodies.  The  only  injury  to  be 
apprehended  from  the  fall  of  the  shutter  is  from  extraneous 


124 


APPENDAGES   OF  DAMS. 


bodies  lying  on  the  dam.  The  props  need  not  be  sacrificed  as 
are  the  boards  in  the  ordinary  arrangement,  as  they  can  be 
attached  to  the  main  chain  and  hauled  in  with  it. 


FIG.  646.  FIG.  64<r. 

Fishways. — Certain  species  of  fish,  dwelling  habitually  in 
salt  water,  are  capable  of  existence  in  fresh  water,  and  are 
endowed  with  an  instinct  which  impels  them  to  ascend  rivers 
at  certain  seasons  of  the  year,  there  to  deposit  their  spawn, 
after  which  they  return  to  salt  water.  The  young  also  return 
to  salt  water,  and  after  reaching  the  age  of  reproduction,  two, 
three,  or  four  years,  return  to  the  grounds  where  their  own 
existence  commenced,  and  revisit  the  same  grounds  annually 
thereafter.  This  fact  has  been  unmistakably  verified  by  the 
United  States  Fish  Commission. 

The  chief  varieties  of  fish  possessed  of  this  characteristic 
are  salmon,  shad,  and  alewives.  So  imperious  is  the  migratory 
instinct  that  no  common  obstacle  can  arrest  the  upward 
progress  of  these  fish.  They  make  their  way  through  foaming 
rapids,  and  easily  surmount  a  perpendicular  fall  of  considerable 
height.  At  Currytunk,*  on  the  Kennebec  River,  there  is  a 
fall  of  i6£  feet,  as  near  perpendicular  as  the  movement  of  the 
water  will  permit,  the  water  falling  into  a  pool  of  great  depth. 
Salmon  have  been  repeatedly  seen  to  jump  this  fall.  They 
apparently  start  from  a  point  deep  in  the  pool,  and,  on  reach- 
ing the  surface,  have  a  velocity  which  carries  them  10  or  12  feet 

*  Report  of  U.  S.  Commission  of  Fish  and  Fisheries,  1872-3. 


FISH 'W -AYS.  125 

out  of  water.  They  thus  strike  the  stream  where  it  has  not 
acquired  a  great  velocity,  and  are  able  to  swim  to  the  upper 
pool  in  the  descending  stream,  the  movement  of  the  fish  being 
more  rapid  than  that  of  the  water.  Ordinarily  5  or  6  feet  is  as 
high  a  fall  as  a  salmon  can  be  expected  to  jump,  and  probably 
somewhat  less  for  the  other  varieties. 

Migratory  fish  ascend  the  streams  in  the  spring  and  early 
summer.  The  salmon  comes  earliest  and  generally  remains 
the  longest,  not  being  ready  to  spawn  till  late  in  the  season. 
Salmon  and  ale  wives  go  farther  up  the  stream  than  the  shad. 
Alewives  push  up  the  smallest  streams,  evidently  in  quest  of 
quiet  water.  Fishermen  take  advantage  of  these  annual  migra- 
tions to  capture  large  numbers  of  the  fish.  The  erection  of  a 
high  dam  across  a  stream  operates  as  an  effectual  barrier  to  the 
ascent  of  fish,  and  is  looked  upon  as  a  great  grievance  by  those 
who  have  depended  upon  the  fisheries. 

The  exclusion  of  migratory  fish  from  the  upper  reaches  of 
streams  has  long  attracted  public  attention,  and  this  was  one  of 
the  facts  which,  thirty  or  forty  years  ago,  led  to  the  appoint- 
ment of  State  fish  commissions  charged,  among  other  things, 
with  the  duty  of  enforcing  the  construction  and  maintenance 
of  fishways  at  dams.  Thirty- two  of  the  States  now  have 
executive  bodies  of  this  kind,  in  addition  to  the  United  States 
Commission  of  Fish  and  Fisheries  acting  on  behalf  of  the 
general  government.  These  agencies  have  succeeded  in  en- 
forcing the  erection  of  fishways  at  most  of  the  important  dams, 
though  they  have  not  always  been  successful  in  securing  their 
maintenance. 

The  erection  and  maintenance  of  fishways  is  less  imperative 
now  than  formerly,  as,  by  the  methods  adopted  by  the  United 
States  Fish  Commission,  the  eggs  of  fish  in  immense  numbers 
are  deposited  and  hatched  in  the  upper  reaches  of  streams, 
compensating  in  some  measure,  though  not  entirely,  for  the 
loss  incident  to  the  stoppage  of  the  annual  migrations. 

A  fishway  is  a  series  of  passages  leading  from  the  upper  to 
the  lower  pool,  large  enough  to  be  easily  traversed  by  the  fish, 


126 


APPENDAGES   OF  DAMS. 


and  so  arranged  as  not  to  give  the  water  a  velocity  sufficient 
to  make  the  passage  difficult.  From  a  2O-foot  dam,  for 
instance,  the  water  falling  freely  or  running  down  a  straight 
incline  reaches  the  lower  pool  with  a  velocity  of  some  36  feet 
per  second,  a  velocity  which  no  fish  can  move  against.  Lead- 
ing the  water  down,  however,  by  a  series  of  falls  of  I 


FIG.  65. 


FIG.  6s«. 


FIG.  66. 


it  nowhere  attains  a  velocity  greater  than  8  feet  per  second,  a 
current  which  any  fish  can  ascend  with  ease.  This  principle 
gives  the  key  to  the  construction  of  the  fish  way. 

The  earliest  form  of  fish  way  is  indicated  at  Fig.  65 ,  and  in 
this  form  was  applied  to  certain  English  rivers  some  sixty  years 
ago.  It  consisted  of  a  channel  leading  down  from  the  crest  of 


FISHWA  YS 


127 


the  dam  at  an  inclination  of  about  I  in  7.  Cross-walls  or  par- 
titions divided  the  channel  into  a  large  number  of  pools,  com- 
municating with  one  another  by  passages  through  the  walls. 
In  this  form  it  was  called  a  salmon-ladder,  being  designed  with 
special  reference  to  that  fish,  and  worked  very  successfully. 


T 


=f) 


FIG.  67. 


=L 


FIG.  68. 


The  figure  shows  the  fish  way  as  forming  a  part  of  the  dam, 
and  of  massive  construction  as  was  frequently  the  case.  The 
application  of  the  fishway  to  English  rivers  in  this  form  is 
attributed  to  James  Smith  of  Deanston,  England,  a  civil  en- 
gineer of  considerable  note  in  the  early  part  of  the  present 
century.  On  American  streams  the  fishway  is  more  commonly 


128  APPENDAGES   OF  DAMS. 

built  of  timber,    either   as  a    cribwork   loaded   with   stone   or 
bolted  to  the  masonry  or  rock. 

The  chief  modification  which  this  model  has  undergone  in 
its  application  to  American  streams  is  in  the  direction  and  form 
of  the  partitions.  In  the  form  shown  at  Fig.  66  it  is  called  the 
Swazy  fishway.  The  inclined  direction  of  the  partition  is 
thought  to  have  some  advantage,  as  offering  the  fish  a  larger 
space  of  dead  water  to  rest  in  when  he  feels  so  disposed.  This 
feature  is  still  further  developed  in  the  form  of  Fig.  67,  which 
represents  a  fishway  erected  on  the  Androscoggin  in  Maine  in 
1870.  In  moving  up  the  stream  the  fish  has  no  other  guide 
than  the  direction  of  the  current,  which  his  instinct  leads  him 
to  swim  against.  This  instinct  leads  him  to  the  foot  of  the 
dam  when  there  is  much  water  going  over  it,  and  there  he  is 
apt  to  remain,  searching  for  some  passage  around  it  or 
exhausting  himself  in  efforts  to  jump  over  it.  A  fishway  lead- 
ing the  water  down  in  a  long  incline  discharges  so  far  from 
the  dam  that  the  fish  does  not  readily  find  the  entrance, 
especially  when  the  discharge  of  the  latter  is  small  compared 
with  that  of  the  dam.  For  this  reason  it  is  advised,  in  the  case 
of  a  high  dam,  to  make  a  return  in  the  fishway,  bringing  the 
discharge  nearer  the  dam,  as  indicated  by  Fig.  68,  where  the 
fish  will  more  readily  find  the  entrance.  Of  course  the  reader 
will  understand  that  in  this  very  general  view  of  the  subject 
we  are  giving  no  heed  to  the  question  of  possible  injury  to  the 
structure  by  water  or  ice  coming  over  the  dam. 

Fig.  69  shows  in  more  detail  a  form  of  fishway  approved 
by  the  United  States  Commission  of  Fish  and  Fisheries.  It  is 
represented  as  applied  to  a  dam  of  cribwork,  but  is  susceptible, 
with  suitable  modifications,  of  application  to  a  dam  of  any 
construction,  and  requires  no  further  explanation  than  is  con- 
tained in  the  following  directions  of  the  Commission : 

Slope  of  fishway  should  not  be  steeper  than  on  a  ratio  of 
i  vertical  to  4  horizontal.  Intake,  or  up-stream  end  offish- 
way,  should  be  amply  large  and  placed  not  less  than  I  foot 
lower  than  the  crest  of  the  dam. 


FISHWA  VS. 


I29 


J30 


APPENDAGES   OF  DAMS. 


FISH "W 'A  YS. 


13' 


Outlet  should  be  below  low-water  level,  and  so  located  or 
constructed  that  fish  are  naturally  led  to  it  when  ascending  the 
stream. 

There  should  be  relatively  deep  water,  with  an  unobstructed 
flow  below  the  outlet  of  the  fishway.  An  ample  discharge  of 
water  should  attract  the  fish  to  the  outlet. 

There  should  be  plenty  of  light  admitted  in  the  fishway, 
and  its  construction  should  be  such  as  to  be  readily  inspected 
and  cleaned  of  any  debris  lodging  therein. 


_MEA_N_H!6H_WAT| 


FIG. 


FIG. 


The  floor  of  the  compartments  should  be  laid  slightly  in- 
clined, and  the  bulkheads  somewhat  obliquely  across  the 
fishway,  so  that  the  current  of  water  passing  through  the  com- 
partments can  more  readily  clear  the  same  of  sand,  mud,  and 
rubbish. 

There  should  be  no  regulating-gates  or  other  devices  at  the 
intake  which  necessitate  the  services  of  an  attendant. 

The  apertures  in  the  bulkheads  should  increase  progressively 
from  the  lower  to  the  upper  ones,  to  insure  overflow  from  com- 
partment to  compartment. 

The  flow  of  water  should  be  abundant,  forming  small  water- 
falls over  the  bulkheads,  so  that  the  fish  may  either  jump  from 
one  compartment  to  the  next  above  or  may  dart  through  the 
apertures  in  the  bulkheads. 

While  the  flow  of  water  through  the  apertures  may  reach  a 
velocity  of  10  feet  per  second,  there  will  be  relatively  quiet 
water  in  the  compartments,  thus  furnishing  a  resting-place  for 
the  ascending  fish. 


132  APPENDAGES   OF  DAMS 

To  maintain  the  operation  of  the  fishway  at  an  average  high 
water  the  same  as  at  the  ordinary  stage  of  the  stream  or  river, 
the  uppermost  compartment  is  made  somewhat  longer,  and  a 
central  bulkhead  is  inserted  having  its  crest  at  the  high-water 
level. 

The  fishway  may  be  constructed  of  wood  or  masonry  and 
iron ;  it  may  follow  a  straight  line  or  be  built  in  angles  and 
curves,  as  the  local  conditions  may  require. 

The  size  of  the  fishway  depends  principally  on  the  volume 
of  water  available,  and  can  be  made  larger  or  smaller  than 
shown  on  plan.  The  hydraulic  head  between  two  successive 
compartments  must  be  so  chosen  as  to  obtain  a  current  velocity 
through  the  apertures  of  not  to  exceed  10  feet  per  second.  At 
low  stage  of  the  stream  or  river,  with  the  fishway  flowing  full, 
there  should  be  a  liberal  discharge  over  the  crest  of  the  dam. 

The  fishway  should  be  built  very  strong  and  be  well  pro- 
tected against  the  destructive  effects  of  freshets,  drift,  ice,  etc. 


CHAPTER    VI. 
MOVABLE   DAMS. 

DAMS  which  can  be  set  up  and  thrown  down  at  will  have 
been  developed  and  brought  to  a  high  state  of  perfection, 
during  the  last  fifty  years,  in  connection  with  river  navigation. 
Their  application  in  projects  of  water-power  is  limited  to  those 
cases  where  dams  are  required  to  be  lowered,  in  whole  or  in 
part,  in  time  of  flood.  As  already  observed  under  the  head  of 
Flashbqards,  the  devices  in  use  for  this  purpose  are  crude  and 
imperfect.  There  are  cases  in  existence,  and  doubtless  many 
more  to  arise  hereafter,  in  which  some  applications  of  the  prin- 
ciples of  movable  dams  might  judiciously  be  made  to  this 
purpose.  For  this  reason  it  is  believed  that  a  glance  at  the 
leading  types  of  movable  dams  will  not  be  a  waste  of  time. 

Fig.  70  shows  the  principle  of  the  bear-trap  dam,  which 


FIG.  70. 

found  many  applications  for  purposes  of  navigation  on  the  rivers 
of  Pennsylvania  in  the  early  part  of  this  century.  Two  con- 
tinuous shutters  or  leaves  extend  entirely  across  the  channel  to 
be  closed,  and  abut  against  smooth  perpendicular  walls  at  the 
ends,  the  walls  forming  the  sides  of  the  channel.  When  the 

133 


134  MOVABLE  DAMS. 

dam   is  not  raised   these  leaves  lie  in  a  recess  in   a   mass   of 
masonry  on  the  bed  of  the  stream,  the  up-stream  leaf  folded 
over  the  down-stream.     The  two  shutters,  in  connection  with 
the  bed  and  end  walls,  form,  at  all  times,  a  closed  chamber 
from  which  the  water  of  the  stream  is  excluded.      To  erect  the 
dam,   water  from  a   higher  level  is  admitted  to  the  chamber 
through  an  opening  in  the  abutment  shown  in  the  drawing. 
Of  course  there  is  a  good  deal  of  leakage,  but  with  a  sufficient 
volume  of  water  the  dam  will  rise  till  the  down-stream  leaf 
reaches  the  limit  of  its  chain.      To  lower  the  dam,  the  supply 
of  water  is  cut  off  and  the  chamber  is  put  in  communication 
with  the  down-stream  channel.      In  the  simple  form  shown  in 
the  figure  this  dam  has  a  marked  advantage  over  every  other 
form  of  movable  dam,  in  its  freedom  from  liability  to  derange- 
ment from  the  intrusion  of  drift  and  sediment — a  consideration 
of  primary  importance  in  structures  of  this  kind.      This  device 
has  been  extensively  applied,  and  almost  every  application  takes 
a  new  form.     Often  the  two  shutters  are  hinged  together  at 
the  summit  and  the  foot  of  the  up-stream  shutter  slides  on  a 
smooth  platform,  the  down-stream  shutter  turning  on  a  fixed 
hinge.     Another  modification  has  the  same  elements,  with  the 
addition  of  a  third  leaf  or  shutter.      This  is  hinged  to  the  bed 
of  the  channel,   at  a  point  near  the  extreme  position  of  the 
sliding  foot,  its  free  end  resting  on  the  up-stream  leaf,  its  pre- 
sumed object  being  to  protect  the  latter  from  drift  and  deposits. 
Another  arrangement  is  like  Fig.  70,  with  the  addition  of  a 
third  leaf  hinged  to  the  top  of  the  up-stream  shutter  and  sliding 
at  the  lower  end.      In  other  systems  the  up-stream  or  down- 
stream leaf  is  in  two  parts  hinged  together,    and    these  fold 
up  when  the  dam  is  down.      These  again  are  combined  with 
sliding  leaves,  etc. 

The  Thenard  Shutters — This  combination  consists  of  two 
sets  of  shutters  extending  entirely  across  the  stream  and  hinged 
to  the  bottom.  The  up-stream  set  fall  up-stream,  and  their 
movement  is  limited  by  chains.  The  down-stream  set  fall 
down-stream,  and  when  up  are  sustained  by  props.  The  dis- 


THE    THENARD    SHUTTERS. 


'35 


tinctive  feature  in  the  working  of  this  system  is  that  the  erec- 
tion of  the  up-stream  set  arrests  the  entire  flow  of  the  stream, 
causing  the  water  to  drop  on  the  down-stream  side,  so  that  the 
set  of  shutters  designed  to  hold  the  water  can  be  raised  and 
secured  before  the  water  rises  so  as  to  overflow  the  up-stream 
set  and  interfere  with  that  operation. 

Fig.  7 1  shows  the  principle  of  this  system  as  applied  to  a 
permanent  dam  of  masonry,  that  being  the  first  application 


FIG. 


FIG.  710. 


FIG.  71. 

which  it  received  and,  so  far  as  the  writer  is  aware,  the  only 
one.  When  the  water  is  not  raised,  both  sets  of  shutters  lie 
flat  on  the  dam.  The  up-stream  set  is  latched  down  securely 
and  the  water  flows  freely  over  both  sets.  To  each  set  of 
shutters  pertains  a  tripping-bar,  not  shown  in  the  cut,  reaching 
the  whole  length  of  the  dam  and  terminating  at  the  abutment, 
where  it  is  coupled  with  devices  enabling  it  to  be  pulled  end- 
wise. A  pull  on  the  up-stream  tripping-bar  releases  all  the 
up-stream  shutters,  which  on  being  released  are  instantly  seized 
by  the  current  and  set  erect  so  far  as  the  chains  will  permit. 


136  MOVABLE  DAMS. 

The  entire  flow  of  the  stream  is  now  stopped  and  the  dam 
becomes  accessible  till  the  water  has  risen  so  as  to  overflow  the 
shutters.  In  this  interval  attendants  erect  the  down-stream 
shutters,  placing  the  feet  of  the  props  in  recesses  prepared  to 
receive  them.  When  the  water  overtops  the  up-stream  shutters, 
and  fills  the  space  between  the  two  sets,  the  up-stream  set  fall 
and  are  latched  automatically.  The  entire  flow  of  the  stream 
goes  over  the  down-stream  shutters,  till  the  latter  are  thrown 
down  by  the  tripping-bar. 

The  Tripping-bar  is  shown  at  Fig.  71  a,  consisting  of  a 
stout  rod  extending  entirely  across  the  channel  to  be  closed  by 
the  shutters,  confined  in  proper  bearings  and  carrying  a  series 
of  projecting  studs.  The  abutment  end  of  the  rod  is  a  toothed 
rack  gearing  with  a  pinion  which  is  operated  by  a  hand-wheel 
on  the  top  of  the  abutment  and  is  susceptible  of  a  movement 
of  several  feet  in  either  direction.  The  studs  of  the  down- 
stream bar  engage  with  the  feet  of  the  props  supporting  the 
shutters,  and  draw  them  successively  off  their  steps,  causing  the 
shutters  to  fall.  These  studs  are  spaced  so  as  to  come  succes- 
sively into  contact  with  the  props — not  all  at  once,  the  bar 
requiring  a  movement  of  an  inch  or  an  inch  and  a  half  to  each 
prop.  In  like  manner  the  studs  of  the  up-stream  bar  release 
the  latches  confining  the  up-stream  shutters,  and  leave  the  latter 
free  to  rise  under  the  action  of  the  current. 

The  Thenard  shutters  have  worked  very  well  in  the  situa- 
tions to  which  they  have  been  applied,  viz.,  as  a  supplement 
to  the  height  of  a  permanent  dam.  Their  application  to  the 
general  purpose  of  a  movable  dam,  where  it  would  rest  upon 
a  mass  of  masonry  level  with  the  natural  bed  of  the  stream, 
is  more  doubtful.  In  the  former  situation,  as  soon  as  the 
up-stream  shutters  are  erected-  the  down-stream  set  is  accessi- 
ble for  raising.  The  permanent  dam  creates  something  of  a 
pond  and  the  water  rises  slowly,  giving  ample  time  for  the 
erection  of  the  down-stream  shutters.  In  the  latter  case  the 
conditions  would  be  different.  The  shutters  when  down  would 
lie  in  a  depth  of  3,  4,  or  5  feet  of  water,  and  to  raise  a  head 


THE  POIREE  NEEDLE  DAM.  137 

of  12  feet  would  have  to  be  from  15  to  18  feet  in  length.  The 
erection  of  the  up-stream  shutters  would  be  attended  with  no 
difficulty.  That  being  done,  the  water  would  commence  to 
rise  on  the  up-stream  side  and  fall  below.  Some  time  must 
elapse  before  the  down-stream  shutters  become  accessible  to 
commence  the  work  of  raising.  Should  any  accident  occur  or 
any  unforeseen  difficulty  arise  to  delay  the  raising  of  the  down- 
stream set  till  the  water  commences  to  run  over  the  up-stream, 
then  the  entire  movement  would  be  blocked.  The  down- 
stream set  could  not  be  raised  nor  the  up-stream  set  lowered. 
To  obviate  this  difficulty  it  is  necessary  to  provide  a  weir  to 
discharge  the  entire  flow  of  the  stream  in  moderate  stages  with- 
out allowing  the  water  to  overtop  the  shutters.  These  difficul- 
ties have  prevented  the  application  of  this  system. to  the  gen- 
eral purposes  of  the  movable  dam. 

The  reader  will  of  course  understand  that  dams  of  the  con- 
struction described  cannot  be  operated  without  a  considerable 
interval  or  clearance  between  the  consecutive  shutters,  and  that 
a  great  volume  of  leakage  must  result.  These  gaps  are  closed 
by  square  pieces  of  scantling,  as  indicated  at  Fig.  Jib,  the 
pressure  of  the  water  holding  the  scantling  firmly  in  its  place. 

We  come  now  to  the  two  forms  of  movable  dam  which 
have  received  the  most  extended  application ;  the  needle  dam 
and  the  wicket  dam.  These  have  one  feature  in  common, 
viz.,  each  requires  a  temporary  foot-bridge  for  its  erection  and 
removal. 

The  Poire'e  Needle  Dam,  so  called  from  its  inventor, 
M.  Poiree,  an  officer  of  the  French  engineer  department, 
was  first  applied  in  France  about  the  year  1834.  A  general 
idea  of  the  device  will  appear  from  Fig.  72,  which  is  an  eleva- 
tion of  the  dam  in  process  of  erection,  Fig.  72*2  a  plan,  and 
Fig.  72^  a  cross-section.  It  is  supposed  to  extend  across  a 
channel  of  any  required  width  with  vertical  side  walls  or  abut- 
ments. One  of  the  abutments  has  a  recess  into  which  the 
adjoining  trestles  fall.  The  construction  and'  manipulation  of 


138 


MOVABLE  DAMS. 


FIG.  72. 


SCALE  OF  FEET 


FIG.  72a. 


THE  POIREE  NEEDLE  DAM.  139 

the  dam  cannot  be  better  described  than  in  the  language  of  the 
inventor :  * 

' '  It  consists  of  a  row  of  trestles  placed  parallel  with  the 
current,  turning  around  their  bases  fixed  to  the  floor,  and  con- 
nected with  one  another  in  the  upper  part,  when  they  are 
upright,  by  clamps  or  bars  having  claws  at  the  end.  Wooden 
needles,  resting  against  the  up-stream  side  on  a  sill  at  the 
bottom  and  on  the  bars  at  the  top,  form  the  wall  which  arrests 
and  sustains  the  water.  When  all  the  trestles  are  bedded  they 
present  no  obstacle  to  navigation  above  the  sill  of  the  floor. 
Each  trestle  is  shaped  like  a  trapezium.  The  two  bases  are 
horizontal ;  the  lower  base  ends  in  journals  which  fit  into  two 
boxes  of  cast  iron ;  the  upper  base  carries  the  planks  of  a  ser- 
vice bridge.  The  up-stream  side  is  vertical,  the  down-stream 
one  sloping.  The  inside  is  furnished  with  a  brace  or  with  other 
•bars  according  to  the  strain  to  be  supported.  At  the  head  of 
the  trestle  is  a  bolt  which  carries  on  its  upper  side  a  washer 
against  which  rests  the  up-stream  bar,  and  having  on  the  lower 
end  a  cap  against  which  is  fitted,  on  one  side  the  curved  claw 
of  the  hook  which  unites  each  trestle  to  the  preceding  one,  and 
on  the  other  side  the  end  of  the  hook  which  joins  it  to  the  one 
following.  Each  hook  is  provided  at  its  extremity  with  a  chain 
which  serves  for  working  it,  and  the  end  of  the  chain  is  fastened 
to  the  cap  of  the  preceding  trestle.  In  order  to  allow  the 
trestles  to  be  easily  worked  by  two  men,  they  are  placed  3.28 
feet  apart  and  are  only  6.23  feet  high,  2.56  feet  wide  at  the 
top,  and  4.92  feet  wide  at  the  base.  The  thickness  of  the  iron 
is  o.  1 2  foot,  and  the  weight  of  each  trestle  is  242  pounds,  with- 
out the  bars  and  hooks.  (This  refers  to  the  Decize  dam,  built 
in  1836.)  When  it  is  necessary  to  raise  the  dam,  two  men 
take  the  chain  which  hangs  along  the  abutment,  raise  the  first 
trestle,  place  its  hook  in  the  ring  fixed  in  the  masonry,  lay  the 
two  planks  on  the  foot-bridge,  and  fasten  the  trestle  to  the 

*See  Thomas  on  Movable  Dams,  Trans.  Am.  Soc.  C.E.,  vol.  xxxix.  p. 
439.  The  description  is  quoted  from  De  La  Grene,  Cours  de  Navigation 
Interieure,  p.  175. 


140  MOVABLE  DAMS. 

coping  by  the  front  and  back  bars.  They  work  in  the  same 
way  with  the  rest  of  the  trestles.  The  skeleton  of  the  dam 
being  up  thus,  the  two  men  proceed  to  fill  it  in  by  placing  the 
needles,  one  by  one,  first  one  space  apart  to  break  the  current, 
then  close  together  to  make  the  wall  as  tight  as  possible.  If 
it  is  desirable  to  lower  the  water,  the  two  men  take  the  needles 
away  one  at  a  time  and  lay  them  on  the  back  part  of  the  foot- 
bridge. If  it  is  desirable  to  remove  the  trestles,  the  needles 
are  taken  to  the  storehouse,  the  bars  and  planks  of  the  last  bay 
are  removed,  then  the  hook  is  raised  which  joins  the  last 
trestle  to  the  last  but  one,  and  it  is  allowed  to  fall,  the  shock 
being  lessened  by  means  of  the  chain  fastened  to  the  hook. 
The  same  method  is  pursued  with  each  bay.  When  each 
trestle  is  laid  down  and  the  chain  stretched,  a  ring  of  particular 
construction  placed  at  a  conveniently  determined  distance 
should  be  on  the  right  of  the  screw-ring  on  the  trestle  still 
standing;  if  such  is  not  the  case,  it  shows  that  the  trestle  is  not 
on  the  bottom. " 

The  above  description  conveys  a  fair  comprehension  of  the 
subject,  though  it  is  not  quite  clear,  by  reason  of  certain  details 
referred  to  not  being  fully  expressed  in  the  drawing.  The 
drawing  represents  the  earliest  application  of  the  system,  which 
did  not  contemplate  a  head  of  more  than  3  feet.  It  has  been 
applied  on  a  larger  and  larger  scale  till  in  its  later  applications 
it  raises  a  head  of  12  or  13  feet.  Many  modifications  have 
been  introduced.  In  the  higher  dams  an  additional  bar  has 
been  introduced  above  the  sill  to  give  the  needles  an  inter- 
mediate bearing-point.  In  some  cases  the  foot-bridge  has  been 
made  continuous,  consisting  of  plates  of  sheet  iron  jointed  to 
the  tops  of  the  trestles,  which  in  that  case  must  be  raised  all 
at  once,  requiring  a  powerful  crab  for  that  purpose.  In  some 
a  track  is  laid  along  the  foot-bridge  on  which  runs  a  truck  to 
fetch  and  carry  the  needles  and  other  materials. 

One  of  the  disadvantages  of  this  system  is  that  it  requires  a 
weir  separate  from  the  movable  dam,  to  discharge  the  flow  of 
the  stream  and  prevent  the  overflow  of  the  foot-bridge. 


THE    CHANOINE    WICKETS.  14! 

Another  is  the  large  amount  of  extraneous  material  to  be 
handled  at  every  manoeuvre  of  the  dam,  and  kept  in  storehouse 
when  the  dam  is  down.  Another  is  the  liability  to  derange- 
ment from  drift.  Should  drift  run  while  the  dam  is  being 
lowered,  or  be  lodged  against  the  dam  on  commencing  to  lower 
it,  it  is  very  liable  to  become  entangled  in  the  trestles  and  pre- 
vent them  from  being  lowered,  in  which  case,  should  the  river 
continue  to  rise,  and  drift  to  increase,  the  dam  is  likely  to  be 
destroyed  or  greatly  injured. 

The  Chanoine  Wickets. — This  form  of  movable  darn, 
shown  in  Fig.  73,  consists  of  a  series  of  wickets  suspended  at 
the  centre,  each  resting  on  a  "horse."  The  horse  is  a  quad- 
rangular frame,  consisting  of  two  legs  jointed  to  the  bottom 
and  rigidly  united  by  a  horizontal  crosspiece.  A  prop  is  artic- 
ulated to  the  crosspiece,  and  when  the  horse  is  up,  the  foot  of 
the  prop  rests  on  a  step.  When  it  is  thrown  off  the  step,  the 
horse  and  prop  lie  extended  on  the  bottom.  The  horizontal 
crosspiece  terminates  in  journals  which  unite  the  frame  to  the 
wicket  by  means  of  journal-boxes  on  the  back  of  the  latter, 
The  wicket  is  thus  susceptible  of  a  considerable  movement 
while  resting  on  the  horse.  A  sill,  suitably  formed  and  secured 
to  the  bed  of  masonry  on  which  the  dam  rests,-  runs  entirely 
across  the  channel.  When  the  wickets  rest  on  this  sill,  the 
channel  is  closed  and  the  water  rises.  When  the  up-stream 
end  of  the  wicket  is  raised  so  as  to  bring  the  latter  into  a  hori- 
zontal position,  the  movement  of  the  water  is  but  slightly 
obstructed  and  the  head  or  lift  disappears.  When  the  prop  is 
tripped  or  thrown  off  its  step,  the  horse  with  its  wicket  and 
attachments  falls  and  all  lie  flat  on  the  bottom,  allowing  boats 
to  float  over  them. 

There  are  two  methods  of  raising  and  lowering  the  dam. 
In  the  earlier  applications  of  the  system  the  wickets  were  raised 
by  a  hoisting  device  carried  on  a  boat,  and  were  thrown  down 
by  a  tripping-bar.  The  arrangement  for  unstepping  the  prop 
is  indicated  by  Figs.  74,  74^,  and  75.  Fig.  74  is  a  plan  and 
Fig.  74#  a  section  of  the  hurter  or  step  and  slide  pertaining 


142 


MOVABLE  DAMS. 


PBI     : 

. 

v--.;-^,;?'-  ':.vA.T 

^•••i^Js£iS3^< 


THE    CHANOINE    WICKETS. 


143 


to  the  prop  when  operated  by  the  tripping-bar.  The  latter  is 
shown  in  section  with  its  stud,  ready  to  take  hold  of  the  foot 
of  the  prop  and  draw  it  off  its  seat,  at  Fig.  74^.  The  shape 
of  the  slide  is  such  that,  while  the  horse  is  falling,  the  foot  of 
the  prop  is  shunted  into  the  path  which  it  is  to  follow  when  the 
FIG.  74- 


SECTION  ON  a  & 

FIG.  740. 


FIG.  75- 

horse  rises.     When  the  horse  is  erect,  the  foot  of  the  prop  falls 
into  its  seat  on  the  hurter. 

As  represented  in  Fig.  73  the  system  involves  a  service- 
bridge  similar  to  that  described  for  the  Poiree  needle  dam, 
consisting  of  a  series  of  trestles  lying  ordinarily  on  the  bottom 
and  susceptible  of  erection  at  will.  With  the  service-bridge, 
the  tripping-bar  is  dispensed  with  and  a  different  form  of 
hurter  is  used.  Fig.  75  shows  the  up-stream  end  of  this 
hurter,  the  remainder  being  identical  with  the  form  of  Figs. 
74  and  74^.  In  this  form  the  horse  is  tripped  by  being  drawn 
a  little  further  up-stream.  This  movement  causes  the  foot  of 
the  prop  to  fall  into  its  descending  path,  in  which  position  it 


144  MOVABLE  DAMS. 

slides  freely  when  the  horse  is  lowered,  and,  as  in  the  former 
case,  is  shunted  so  that  when  the  horse  is  down,  the  foot  of  the 
prop  lies  in  the  path  which  it  is  to  follow  in  rising. 

When  it  becomes  necessary  to  raise  the  dam,  the  service- 
bridge  is  set  up;  on  this  bridge  a  light  railroad-track  is  laid  on 
which  runs  a  truck  carrying  hoisting-gear.  The  hoisting-rope 
or  chain  is  made  fast  to  the  ring  in  the  up-stream  end  of  the 
wicket  and  hauled  in.  The  wicket  rises,  bringing  up  the  horse 
and  prop  till  the  latter  falls  into  its  seat  on  the  hurter,  when 
the  whole  stands  firmly.  By  slacking  off  on  the  winch,  the 
end  of  the  wicket  comes  down  upon  its  seat  on  the  sill.  When 
•the  wickets  are  all  up,  the  water  rises  and  overflows  them.  The 
service-bridge  is  usually  dismantled  and  lowered  when  the  dam 
is  up.  It  is  manifest  that  the  axis  on  which  the  wicket  turns 
may  be  so  placed  that  the  wicket  will  swing  automatically  when 
the  water  rises  to  a  certain  height.  Heavy  floating  bodies  may 
also  swing  the  wicket  and  pass  over,  leaving  the  wicket  to  right 
itself. 

When  occasion  arises  to  lower  the  dam,  the  service-bridge 
is  set  up  as  before,  and  the  hoisting-gear  is  attached  to  the  top 
of  the  wicket.  It  is  drawn  up-stream  a  little  as  indicated  by 
the  dotted  lines,  causing  the  prop  to  fall  into  its  return  path. 
Then  the  wicket  may  be  eased  down  or  let  go  by  the  run,  which 
is  perfectly  safe  as  the  resistance  of  the  water  prevents  any 
shock.  After  lowering  the  wickets  the  service-bridge  is  dis- 
mantled and  lowered,  leaving  the  channel  free  for  the  passage 
of  boats. 

In  order  that  the  wickets  may  work  with  certainty,  a  clear- 
ance of  an  inch  or  two  is  required,  occasioning  considerable 
leakage.  In  works  of  navigation  this  is  not  objectionable  so 
long  as  there  is  plenty  of  water.  When  the  leakage  threatens 
to  diminish  the  head  it  is  stopped  by  the  insertion  of  square 
scantling  as  at  Fig.  jib. 


CHAPTER    VII. 
RESERVOIR-DAMS.     STORAGE-RESERVOIRS. 

THE  requirements  of  modern  industry  are  best  subserved 
by  a  uniform  supply  of  power,  a  necessity  in  no  wise  conform- 
able to  the  natural  flow  of  streams,  as  is  apparent  in  Table  I. 
The  flow  of  all  streams  not  controlled  by  natural  or  artificial 
reservoirs  is  liable  to  at  least  twentyfold  variations.  In  fact  no 
such  stream  except  the  Mississippi  in  its  lower  reaches  shows 
variations  so  small  as  twentyfold.  For  smaller  streams  the 
variations  increase  as  the  drainage-area  diminishes  till  we  come 
to  streams  of  two  or  three  square  miles,  in  which  the  variations 
are  absolutely  infinite,  such  streams  running,  at  times,  entirely 
dry.  This  statement  only  applies  to  the  northeastern  section 
of  the  United  States.  In  the  southwesterly  parts  streams 
commanding  hundreds  of  square  miles  are  often  dry  for 
months. 

The  distribution  of  the  flow  of  streams  throughout  the  year 
is  stated  'on  page  4. 

These  figures  would  be  modified  somewhat  by  the  latitude. 
In  northern  Maine  we  should  put  the  maximum  flow  about  a 
month  later  and  in  Pennsylvania  about  a  month  earlier  than 
given  on  page  4.  This  statement  shows  in  a  strong  light 
the  chief  defect  of  water-power,  viz.,  its  extreme  variability. 
A  stream  furnishing  1000  horse-power  during  the  five  wettest 
months  could  not  be  counted  on  for  more  than  200  during  the 
driest,  viz.,  in  July.  In  reality  not  so  much  as  this,  since  the 
figure  for  July,  2  per  cent,  being  the  average  of  a  series  of  years, 
there  will  be  Julys  in  which  the  flow  will  fall  below  2  per  cent, 
and  days  in  the  same  month  on  which  it  will  fall  lower  still. 

145 


146  RESERVOIR-DAMS.     STORAGE-RESERVOIRS. 

An  industrial  plant  operated  wholly  by  water-power,  and  sub- 
ject to  the  necessity  of  running  at  a  uniform  rate,  could  not 
make  rational  use  of  more  than  20  per  cent  of  the  total  flow 
of  a  natural  stream. 

There  are  two  modes- of  meeting  this  difficulty.  The  more 
common  one,  which  will  be  considered  later,  is  by  the  installa- 
tion of  a  reserve -of  steam-power  for  reliance  during  the  dry 
months.  There  are  situations,  however,  where  the  construc- 
tion of  storage-reservoirs,  to  hold  the  superfluous  waters  of  wet 
months  for  use  during  the  dry,  is  more  economical  than  steam- 
power,  and  still  other  situations  in  which  such  a  proceeding  is 
advisable  though  it  may  not  wholly  obviate  the  use  of  steam- 
power. 

Storage-reservoirs,  or  reservoirs  designed  to  hold  the  water 
of  seasons  of  abundance  for  use  during  seasons  of  scarcity,  are 
built  for  several  different  purposes,  viz.:  (i)  for  municipal 
water-supply;  (2)  for  irrigation;  (3)  for  navigation  properly 
so  called,  that  is,  for  the  supply  of  canals  or  to  maintain  the 
depth  of  water  in  natural  channels;  (4)  for  log-driving;  (5)  for 
water-power.  The  first-named  purpose  is  closely  connected 
with  the  health,  comfort,  and  prosperity  of  great  communities, 
and  warrants  expenditures  which  would  generally  be  unjustifi- 
able in  connection  with  water-power.  Nevertheless  these 
reservoirs  are  valuable  in  the  present  connection  as  exhibiting 
the  principles  of  construction  perhaps  more  clearly  than  any 
other  class.  Reservoirs  for  the  four  last-mentioned  purposes 
may  all  be  classed  together,  except  that  the  fourth  class  is 
usually  provided  with  outlet-sluices  larger  than  are  necessary 
for  any  other  purpose. 

A  reservoir-dam  has  these  parts: 

1 .  The  body  or  mass,  which  gives  solidity  to  the  dam  and 
enables  it  to  resist  the  pressure  of  the  water. 

2.  The  skin  or  diaphragm,  which  arrests  the  movement  of 
the  water  through  the  dam.     This  element  is  sometimes  want- 
ing when  the  body  of  the  dam  is  of  uniform  and  homogeneous 
material. 


LOCATION   OF  RESERVOIRS.  147 

3.  The  outlet-sluice,  which  enables  the  water  to  be  dis- 
-charged  according  to  necessity. 

4.  The  wasteway,  for  the  discharge  of  superfluous  water. 
Location  of  Reservoirs. — The  earth's  surface  presents  to 

the  general  view  a  series  of  ridges,  a  conformation  referred  by 
geologists  to  shrinkage  of  the  earth's  crust  in  cooling  from  a 
molten  state.  This  agency  has  defined  the  great  salient  features 
of  topography,  continental  elevations,  mountain  ranges,  and 
the  general  course  of  streams.  The  surface  thus  rough-hewn 
has  been  carved,  eroded,  and  brought  to  its  present  form  by 
the  agencies  of  air,  water,  and  frost.  The  air  has  operated 
chiefly  by  oxidizing  certain  elements  of  exposed  rocks  and 
reducing  them  to  soils  and  gravels.  Water  has  diversified  the 
contours  by  carrying  away  soils,  gravels,  and  rocks,  and,  acting 
through  the  immeasurable  periods  of  geologic  time,  has  trenched 
the  earth  with  channels  and  canyons.  Gaining  access  to 
highly  heated  rocks,  it  has  reduced  them  to  sands.  Set  in 
motion  by  the  winds,  it  has  worn  dawn  rocky  shores,  tossed 
the  fragments  to  and  fro  upon  beaches,  and  ground  them  to 
clay  which  it  has  spread  over  wide  areas  to  be  subsequently 
hardened  into  rock.  It  has  nourished  the  myriads  of  insects 
whose  microscopic  shells  falling  to  the  bottom  have  aggregated 
into  great  geologic  strata.  Frost  also  has  played  its  part  in 
the  disintegration  of  rocks  by  congealing  the  water  in  their 
crevices  and  causing  it  to  expand  with  irresistible  force.  Like- 
wise in  the  formation  of  glaciers  which  have  crept  slowly  over 
the  land  armed  with  rocky  fragments  firmly  grasped  to  aid 
their  erosive  action,  and  finally,  under  changed  climatic  condi- 
tions, have  dissolved  in  enormous  floods  and  deposited  the 
accumulations  of  thousands  of  years  in  glacial  moraines. 

A  storage-reservoir  is  almost  invariably  constructed  by 
throwing  a  dam  across  the  valley  of  a  stream,  with  the  addition 
sometimes  of  dikes  or  embankments  to  close  lateral  outlets. 
In  forming  a  judgment  of  the  availability  of  any  reservoir-site, 
some  knowledge  of  the  principles  of  geology  is  of  the  greatest 
importance.  The  engineer  should  make  himself  acquainted 


1 48  RESER  V01R-D  A  MS.     S  TOR  A  GE-RESER  V  OIRS. 

with  the  geological  history  and  character  of  the  region.  These 
are  usually  to  be  learned  from  the  geological  surveys  which 
have  been  conducted  under  authority  of  the  several  States,  and 
the  more  comprehensive  survey  now  going  on  under  authority 
of  the  general  government.  Such  knowledge,  if  it  serve  on 
other  purpose,  will  at  least  enable  the  engineer  to  conduct  his 
examinations  understandingly.  To  the  trained  geologist  the 
exterior  configuration  of  the  ground  is  a  pretty  good  indication 
of  what  lies  below,  and  a  knowledge  of  these  principles  shows 
the  engineer  where  to  look  for  the  faults,  dislocations,  and 
anomalies  of  structure  which  sometimes  impair  the  value  of 
reservoirs. 

The  most  favorable  locations  for  reservoir-dams  are  the 
outlets  of  existing  lakes,  or  of  marshes,  which  are  ancient  lakes 
that  have  been  filled  up  by  river  sediment  and  decayed  vegeta- 
tion. Reservoirs  for  municipal  purposes  are  usually  forced  by 
considerations  of  proximity  and  availability  into  other  situa- 
tions, and  also  avoid  marshes  for  sanitary  reasons..  Irrigation- 
reservoirs  do  not  occur  in  regions  where  lakes  and  marshes 
abound.  Dams  for  these  purposes,  therefore,  often  occupy 
narrow  valleys  with  steep  declivities  and  abrupt  sides,  and  are 
necessarily  very  high  to  impound  any  considerable  quantity  of 
water.  To  show  the  enormous  difference  in  cost  between 
different  sites,  it  may  be  mentioned  that  the  system  of  reservoirs 
constructed  by  the  United  States  Government  on  the  head- 
waters of  the  Mississippi,  by  damming  the  outlets  of  several 
lakes,  cost  at  the  rate  of  nine  dollars  per  million  cubic  feet  of 
storage  capacity,  while  the  reservoir  now  contemplated  for  the 
metropolitan  water-supply  of  Massachusetts,  to  be  formed  by 
a  dam  across  the  valley  of  the  Nashua  River,  will  cost  not  less 
than  one  thousand  dollars  per  million  cubic  feet. 

The  entire  northern  region  of  the  United  States  abounds  in 
lakes  and  marshes  or  wet  meadows.  When  these  occur  near 
the  headwaters  of  the  streams  they  command  but  little  drain- 
age-area and  are  of  little  value  for  the  purpose  in  view.  Their 
occurrence  at  points  where  the  stream  has  attained  a  consider- 


EMBA  NKMEN  TS.  1 49 

able  volume  is  rarer,  but  still  not  uncommon.  In  forest  regions 
during  the  early  stages  of  the  country's  settlement  such  sites 
are  usually  seized  upon  by  lumbermen  for  sluicing-dams. 
Later,  after  the  exhaustion  of  the  timber,  they  are  applied  to 
purposes  of  water-power. 

A  natural  lake  is  often  formed  in  the  course  of  a  running 
stream  by  the  slow  rising  of  the  rock  through  volcanic 
agencies,  in  a  line  crossing  the  stream.  The  wearing  of  the 
rock  by  the  action  of  the  stream  keeps  pace,  in  some  degree, 
with  the  rising  of  the  ground,  so  that  we  now  find  the  outlet 
underlain  by  firm  rock  flanked  on  either  side  by  solid  walls  of 
rock.  At  Marble  Falls,  on  the  Colorado  River  in  Texas,  this 
process  is  clearly  traceable.  The  river  flows  for  a  mile  or  more 
between  two  walls  rising  almost  vertically  to  a  height  of  some 
200  feet,  the  dip  of  the  exposed  strata  showing  the  history  of 
its  formation  unmistakably.  Above  this  canyon  the  valley 
spreads  out  into  a  wide  expanse,  and  at  the  foot  of  it  are 
immense  banks  of  loose  rock.  The  surface  rock  on  the  top  of 
the  cliffs  is  worn  by  water.  Localities  of  this  character  form 
the  best  sites  for  reservoir-dams.  On  the  other  hand  lakes 
frequently  owe  their  origin  to  the  obstruction  of  river  valleys 
by  glacial  deposits,  and  in  this  case  the  bed-rock  is  usually 
found  covered  to  a  greater  or  less  depth  by  gravel  or  sand. 

On  a  rock  bottom  or  where  the  rock  is  accessible  at  no 
great  depth  it  is  usually  advisable  to  build  a  dam  of  masonry, 
though  where  economical  considerations  control  and  the  height 
is  moderate  a  structure  of  timber  and  stone  is  not  inadmissible. 
For  a  dam  on  a  sand  or  gravel  formation  an  earth  embankment 
is  more  commonly  adopted. 

Embankments. — Fig.  76  represents  a  form  of  low  embank- 
ment very  common  in  New  England  fifty  to  one  hundred  years 
ago.  It  is  confined  by  two  side  walls  of  split  stone  laid  with- 
out mortar,  which  appear  to  have  no  other  object  than  to 
prevent  the  slopes  from  spreading  out  as  wide  as  they  otherwise 
would.  Above  the  walls  the  earth  was  carried  up  in  slopes 
generally  of  i^  to  i  to  a  width  of  9  to  12  feet  on  top.  There 


150 


RESER  VOIR-DA  MS.     S  TOR  A  GE-RESER  VOIRS. 


is  no  reason  to  suppose  that  the  earth  was  consolidated  in  any 
other  manner  than  by  the  passage  of-  teams  and  carts.  This 
construction  was  never  applied  to  a  head  of  more  than  10  or 
1 2  feet.  A  failure  of  this  form  of  embankment  has  never  come 
to  the  writer's  knowledge. 

Fig.  77  shows  the  more  common  form  of  earth  embank- 


FIG.  76. 


FIG.  77. 

ment,  especially  a  high  embankment,  by  which  I  would  imply 
a  height  of  not  less  than  25  feet.  It  shows  a  wet  slope  of  3 
to  i ,  a  dry  slope  of  2  to  I ,  a  width  of  1 5  feet  on  top,  exclusive 
of  pavement,  the  summit  4  feet  above  high  water,  and  is  pro- 
vided with  a  puddle-wall  in  the  middle  3  to  6  feet  thick  at  the 
top  and  widening  about  I  foot  in  6  downward.  In  considering 
the  material  of  embankments,  we  divide  all  natural  earths  into 
two  general  classes,  viz.,  binding  and  non-binding,  i.e.,  those 
which  are  susceptible  of  consolidation  by  pressure  and  those 
which  are  not.  It  is  well  known  that  sand,  and  gravel  com- 
posed of  sand  and  pebbles,  cannot  be  consolidated  by  pressure, 
neither  does  this  material  retain  the  shape  impressed  on  it  by 
pressure,  although  when  removed  from  its  natural  bed  and 


E  MBA  NKMEN  TS.  1 5 1 

redeposited  it  undergoes  considerable  settlement  in  the  course 
of  time.  On  the  other  hand,  material  containing  a  sufficient 
percentage  of  clay  can  be  moulded  into  any  desired  shape  and 
is  very  susceptible  of  compression  and  consolidation,  qualities 
which  fit  it  for  use  in  water-tight  embankments.  Pure  clay, 
though  one  of  the  most  impervious  of  earths,  has  disadvantages 
in  application  to  situations  liable  to  be  alternately  wet  and 
dry.  In  drying  it  shrinks  greatly  and  presents  crevices  through 
which  the  water,  on  the  occasion  of  a  sudden  rise,  is  liable  to 
find  its  way,  and,  before  the  material  becomes  saturated,  to 
enlarge  the  passages  beyond  the  possibility  of  closing.  The 
same  reason  which  makes  pure  clay  inapplicable  to  bricks, 
tiles,  and  pottery,  forbids  its  use  in  embankments.  It  is 
generally  not  difficult  to  find  in  the  immediate  vicinity  of  a 
proposed  dam  material  suitable  for  embankments. 

The  traditional  mode  of  forming  embankments,  omitting 
for  the  present  the  consideration  of  the  puddle-wall  and  the 
sluices,  is  as  follows:  First  remove  all  vegetable  soil,  tree- 
roots,  and  loose  materials  from  the  site.  Spread  the  embank- 
ment earth  in  layers  6  to  9  inches  deep,  keep  it  moistened  and 
roll  it  with  a  heavy  roller.  Commence  with  the  lowest  part  of 
the  work  and  maintain  the  layers  approximately  level,  except 
that  it  is  thought  advisable  to  give  them  a  slight  inclination 
toward  the  centre  of  the  embankment.  It  is  not  certain, 
however,  that  any  advantage  results  from  this  disposition.  As 
to  the  amount  of  moisture  to  be  supplied,  the  earth  should  by 
no  means  be  reduced  to  a  pasty  condition,  but  should  be  moist 
enough  to  be  readily  squeezed  into  any  desired  form  in  the 
hand,  and  should  not  readily  lose  its  form. 

As  to  the  slopes,  they  should  not  in  any  important  work 
be  greater  than  2  to  I .  It  is  more  common  to  give  the  water- 
slope  a  declivity  of  3  to  I  and  even  4  to  I,  but  for  really  suit- 
abl-e  material  there  seems  no  good  reason  for  a  flatter  slope 
than  2  to  i .  The  water-slope  is  usually  paved  with  heavy 
blocks  of  stone.  The  necessity  for  this  feature  depends  upon 
the  exposure  of  this  face  to  the  action  of  waves.  Where  the 


152  RESERVOIR-DAMS.     STORAGE-RESERVOIRS. 

water-slope  faces  a  broad  and  deep  expanse  of  water  the  pave- 
ment cannot  safely  be  omitted.  Where  the  body  of  the  reser- 
voir is  at  some  distance  from  the  dam,  approached  by  a  narrow 
channel,  the  pavement  is  less  important.  In  the  former  case 
the  height  of  the  embankment  should  not  be  less  than  5  feet 
above  the  crest  of  the  wasteway.  Pavements  usually  consist 
of  rectangular  blocks  of  split  stone  1 2  to  1 8  inches  thick,  rest- 
ing on  a  layer  of  broken  stone  about  6  inches  thick.  This 
arrangement  is  usually  adopted  in  municipal  reservoirs,  and  is 
in  that  case  partly  designed  to  prevent  the  water  from  becom- 
ing muddy  under  the  action  of  winds,  as  well  as  to  prevent  the 
wearing  of  the  embankment  by  waves  acting  through  the 
crevices  of  the  pavement.  This  feature  may  be  omitted,  for  the 
purpose  in  view,  when  the  material  of  the  embankment  contains 
a  large  proportion  of  pebbles. 

Puddle. — It  is  the  ordinary  practice  to  provide  an  embank- 
ment with  a  specially  impervious  layer,  stratum,  or  diaphragm 
composed  of  puddle.  This  is  usually  prepared  by  adding  a 
proper  proportion  of  pure  clay  to  the  material  of  which  the  dam 
is  composed.  In  this  operation  a  pug-mill  similar  to  that 
used  in  brick-making  may  be  employed  with  advantage.  The 
puddle  is  brought  to  the  consistency  of  brick-clay  when  ready 
for  moulding,  and  generally  no  attempt  is  made  to  consolidate 
it  after  depositing.  A  puddle-wall  is  the  name  applied  to  a 
core  of  puddle  carried  up  through  the  embankment  and  keep- 
ing pace  with  the  latter  while  under  construction.  A  trench, 
in  this  case,  is  sunk  along  the  centre-line  of  the  embankment 
to  a  sufficiently  firm  and  impervious  stratum.  Often  great 
expense  is  incurred  in  this  feature  of  the  work,  and  the  trench 
reaches  down  50,  75,  or  even  100  feet  to  solid  rock,  in  which 
case  the  wall  or  core  is  of  uniform  thickness  below  the  surface 
of  the  ground. 

The  impervious  diaphragm  sometimes  consists  of  a  layer  of 
puddle  spread  on  the  water-face  of  the  embankment  and  joining 
a  puddle-trench  near  the  inner  toe.  This  is  preferable  on  some 
accounts  to  the  puddle-wall,  especially  during  construction,  as- 


THE   OUTLET.  153 

the  arrangements  for  depositing  the  puddle-wall  are  something 
of  an  embarrassment  and  hindrance  to  the  rest  of  the  work. 
The  face-puddle  is  not  applied  till  the  embankment  is  finished,, 
the  work  is  exposed  to  view,  and  it  is  easier  to  detect  defects. 
In  contract  work  this  is  a  point  of  importance.  The  objection 
that  this  mode  is  more  expensive  is  not  well  founded.  It  is 
true  that  the  area  of  the  slope  is  two  or  three  times  that  of  the 
midsection,  but  in  this  situation  the  depth  of  puddle  need  not 
be  great;  18  inches  is  as  effective  as  any  greater  depth.  Face- 
puddle  with  pavement  should  not  be  applied  on  a  slope  steeper 
than  2  to  i,  to  avoid  risk  of  slipping.  Where  pavement  is 
applied  to  face-puddle  the  layer  of  broken  stone  should  not  be 
omitted.  Where  the  ground  is  favorable  to  the  driving  of  sheet- 
piles,  that  is,  free  from  large  boulders  and  buried  timber,  a  row 
of  sheet-piling  may  advantageously  take  the  place  of  the  puddle- 
trench.  Face-puddle  has  a  great  advantage  over  a  puddle- 
wall  as  regards  strength  of  the  embankment.  This  is 
especially  true  when  the  body  of  the  embankment  is  composed 
of  porous  gravel,  and  reliance  is  placed  mainly  on  the  puddle 
for  tightness.  In  the  case  of  the  puddle-wall,  the  full  pressure 
of  the  water  acts  against  the  latter,  and  only  half  the  mass  of 
the  embankment  is  available  to  resist  this  pressure.  In  fact 
the  down-stream  half  of  the  embankment  has  to  resist  the 
pressure  of  the  up-stream  half  in  addition  to  the  full  pressure 
of  the  water.  This  pressure  moreover  acts  horizontally,  tend- 
ing to  shove  the  lower  half  of  the  embankment  down-stream. 
In  the  case  of  face-puddle  the  pressure  is  resisted  by  the  entire 
mass  of  the  dam,  and  the  downward  component  of  this  pressure 
tends  to  hold  the  dam  in  place. 

The  Outlet. — This  is  the  most  difficult  feature  of  the  earth 
embankment.  The  failure  of  the  Dale  Dike  Embankment  near 
Sheffield,  England,  in  March,  1864,  by  which  some  two 
hundred  persons  lost  their  lives,  was  traced  to  the  breaking  of 
the  discharge-pipes  through  the  settlement  of  the  embankment. 
More  failures  of  reservoirs  have  occurred  from  defective  outlets 
than  from  any  other  cause.  It  is  to  be  expected  that  some 


154  RESERVOIR-DAMS,     STORAGE-RESERVOIRS. 

settlement  will  take  place  in  the  embankment,  as  well  as  in 
the  ground  on  which  it  rests.  If  the  outlet-pipes  are  laid  upon 
unyielding  supports  such  as  piles,  the  latter  are  liable  to  cause 
ruptures  or  cavities  in  the  embankment.  When  cast-iron  pipes 
are  used  they  should  be  put  together  with  a  view  to  some 
yielding  in  the  joints.  They  should  always  be  laid  on  natural 
earth,  not  on  filled  ground,  and  especially  not  on  ground  partly 
filled  and  partly  natural.  Broad  flanges  are 
applied  at  intervals  to  prevent  the  water  from 
following  the  outside  of  the  pipe,  which  it  is 
very  liable  to  do,  especially  along  the  under 
side,  where  it  is  difficult  to  consolidate  the 
earth.  The  arrangement  of  Fig.  78  has 
been  suggested  as  combining  a  broad  flange 
FIG.  78.  to  prevent  the  creeping  of  the  water  along 

the  pipe  with  a  considerable  yielding  of  the  joint  to  conform  to 
the  settlement  of  the  earth.  The  pipe  is  put  together  with 
flanges,  and  at  each  joint  is  inserted  a  disk  of  3-inch  pine  plank, 
with  an  opening  in  the  centre,  the  exact  size  of  the  pipe,  and 
an  external  radius  some  1 8  inches  greater.  This  is  fitted  to  the 
joint  after  the  pipe  is  bedded,  and  is  bored  with  holes  for  the 
bolts  that  unite  the  consecutive  lengths.  The  wood  is  always 
wet  and  so  preserved  from  decay,  and  it  admits  of  considerable 
compression  without  losing  its  integrity.  In  a  3O-inch  pipe  put 
together  in  12-foot  lengths,  a  compression  of  £  inch  in  the  wood 
implies  a  deflection  of  more  than  2  inches  in  the  pipe,  which  is 
greater  than  ever  need  be  expected.  The  gate  or  valve  for 
controlling  the  discharge  is  placed  sometimes  on  the  land  side, 
sometimes  on  the  water  side.  The  former  has  great  advantage 
in  point  of  simplicity  and  accessibility,  but  in  this  case  the  pipe,  ' 
above  the  valve,  is  under  full  pressure,  and  any  crack  is  liable 
to  cause  great  injury  to  the  embankment.  The  placing  of  the 
valve  on  the  water  side  usually  involves  a  mass  of  masonry 
built  up  to  the  high-water  level,  and  accessible  by  a  bridge 
from  the  embankment.  In  municipal  reservoirs  of  later  con- 
struction this  masonry  usually  takes  the  form  of  a  gate-chamber, 


THE    OUTLET.  I $5 

near  enough  to  the  crown  of  the  embankment  to  be  accessible 
without.a  bridge.  Such  chambers*  are  often  of  very  complex 
construction  and  need  not  be  considered  here.  In  some  of 
the  older  reservoirs  the  outlets  were  very  simply  and  efficiently 
managed  by  extending  the  pipe  to  the  foot  of  the  water-slope 
and  there  providing  it  with  a  flap-valve  operated  by  a  chain 
running  up  the  slope  to  a  windlass  on  the  crown  of  the  em- 
bankment. The  placing  of  the  gates  on  the  water  side  of  the 
embankment  is  coupled  with  the  great  advantage  that  the 
interior  of  the  sluice  can  be-  rendered  accessible  for  inspection 
if  of  sufficient  size  to  admit  an  observer,  which  it  would  be  in 
any  work  of  importance. 

In  embankments  under  30  feet  in  height  siphon-pipes  have 
been  successfully  employed,  and  have  shown  in  some  respects 
decided  advantages  over  every  other  mode  of  discharge.  The 
pipe  has  its  influx  near  the  foot  of  the  inner  slope,  protected 
by  a  screen  to  exclude  floating  bodies,  passes  up  the  inner  and 
down  the  outer  slope,  discharging  into  a  basin  sufficiently 
extensive  to  moderate  the  commotion  of  the  water.  It  is 
advisable  to  cover  the  pipe  with  puddled  earth  both  on  the 
inner  and  the  outer  slope,  not  only  for  protection  against  frost, 

*  It  is  a  singular  fact  that  almost  all  important  municipal  reservoirs, 
storage  or  service,  of  recent  construction,  have  been  provided  with  com- 
plex and  expensive  arrangements  for  drawing  water  from  different  depths, 
by  opening  orifices  at  surface,  mid-depth,  full  depth,  etc.,  according  to 
requirement.  It  may  be  a  fact  that  the  water  of  mid-depth  is  at  times 
preferable  to  that  of  the  bottom  or  surface,  and  rice  -versa,  but  it  appears 
to  me  that  the  engineer  who  expects  the  discharge  of  an  orifice  at  mid- 
depth  of  a  reservoir  to  be  confined  to  water  lying  at  or  near  that  depth 
is  presuming  somewhat  upon  the  obliging  disposition  of  this  element. 
When  an  orifice  is  opened  in  the  vertical  side  of  a  reservoir,  any  particle 
of  water  nearer  the  orifice  than  the  nearest  boundary  of  the  reservoir 
moves  directly  toward  the  orifice,  whether  its  path  be  upward,  downward, 
or  horizontal.  There  is  no  conceivable  reason  why  it  should  move  more 
readily  in  one  direction  than  another.  So  that  an  orifice  at  mid-depth, 
after  discharging  a  hemisphere  of  water  whose  radius  is  the  semidepth,  is 
discharging  an  exact  mixture  of  all  the  horizontal  strata,  top,  bottom,  and 
middle.  An  orifice  at  the  surface  or  bottom  would  arrive  at  this  condi- 
tion after  discharging  a  quarter-sphere  whose  radius  is  the  full  depth. 


156  RESERVOIR-DAMS.     STORAGE-RESERVOIRS. 

but  to  prevent  the  influx  of  air  through  the  joints.  When  the 
crown  of  the  reservoir  is  above  the  highest  level  of  the  water 
no  gate  is  necessary,  the  flow  being  established  by  the  exhaus- 
tion of  air  and  arrested  by  its  admission.  A  gate  or  valve, 
however,  is  generally  inserted  for  the  purpose  of  regulating  the 
quantity  of  water  discharged.  It  is  manifest  that  the  height  of 
the  crown  of  the  siphon  above  low  water  cannot  exceed  the 
height  due  to  atmospheric  pressure,  viz.,  about  34  feet.  Prac- 
tically it  is  considerably  less,  and  25  feet  is  about  as  great  a 
lift  as  can  be  adopted.  Fig.  79*' shows  an  outlet  of  this  form 


iftr 

FIG.  79. 

as  applied  to  one  of  the  Bann  reservoirs  near  Dublin,  Ireland. 
The  success  of  this  method  requires  efficient  means  constantly 
in  readiness  for  exhausting  the  air  from  the  summit  of  the 
siphon.  Air  enters  through  crevices  which  would  hardly  show 
a  trace  of  leakage  of  water.  A  small  orifice  under  atmospheric 
pressure  will  pass  twenty-eight  times  as  great  a  volume  of  air 
as  of  water.  In  addition  to  this,  absolute  tightness  of  the  pipe 
does  not  obviate  the  necessity  for  the  withdrawal  of  air. 
Water  absorbs  air  under  pressure,  and  eliminates  it  when  the 
pressure  is  diminished.  Water  passes  the  crown  of  the  siphon 
under  a  reduced  pressure  and  is  constantly  giving  out  air.  which 
must  be  constantly  withdrawn  in  order  to  maintain  the  efficiency 
-of  the  siphon.  The  best  proceeding  is  to  adapt  to  the  efflux 
of  the  siphon  a  small  simple  water-wheel,  driving  an  air-pump, 
fitted  by  means  of  a  small  pipe,  to  draw  the  air  from  the 
summit  of  the  siphon.  Even  this  arrangement  does  not  obviate 

*  Description  of  the  Bann  Reservoir  by  Mallet  in  Weale's  Quarterly 
Papers  on  Engineering,  vol.  vi.  part  I.  The  figure  is  taken  from  Hagen's 
Wasserbaukunst,  PI.  LXXVI. 


THE    WASTEWAY.  157 

the  necessity  of  manual  labor  to  set  the  water  in  motion  after 
it  .has  been  stopped  and  the  siphon  partly  filled  with  air. 

The  Wasteway. — This  feature  is  the  safety-valve  of  the 
embankment,  its  function  being  to  discharge  the  surplus  water 
and  prevent  the  water  from  rising  so  as  to  overtop  the  embank- 
ment, which  would  result  in  the  speedy  destruction  of  the  latter. 
Writers  on  these  subjects  sometimes  attempt  to  give  rules  for 
the  width  of  wasteways  depending  on  the  extent  of  the 
drainage-area  tributary  to  the  reservoir.  No  formula  of  this 
kind  can  be  given  with  any  approach  to  correctness.  The 
drainage-area  can  be  determined  with  sufficient  exactness. 
The  maximum  rainfall  to  be  expected  may  be  ascertained 
within  some  reasonable  limits.  But  the  inflow  of  the  reservoir 
consequent  upon  a  given  rainfall  depends  too  largely  upon 
local  conditions  to  be  made  the  subject  of  any  general  state- 
ment-. In  a  mountainous  region,  bare  of  trees,  water  is  dis- 
charged into  the  streams  with  great  rapidity.  In  a  flat  country 
abounding  in  swamps  and  forests  it  is  delayed  so  much  that 
there  is  no  analogy  between  the  two  cases.  The  width  of  the 
wastevvay  will  also  depend  upon  the  surface-area  of  the  reser- 
voir. It  is  a  question  to  be  determined  from  the  special  condi- 
tions of  each  individual  case. 

A  rainfall  *  of  6  inches  in  24  hours  has  been  frequently 
observed.  Instances  are  on  record  of  9  inches,  but  rain  never 
falls  unintermittently  at  this  rate  for  so  long  a  period.  The 
rate  will  at  times  during  the  storm  much  exceed  this  figure,  at 
other  times  fall  much  short  of  it.  Such  variations  can  only  be 
detected  by  self-registering  rain-gauges.  On  the  2ist  of 
August,  1860,  the  rain-gauge  at  Waltham,  Mass.,  showed  a 
fall  of  5.63  inches  in  3  hours.  At  St.  Louis  there  is  a  record 
of  4  inches  in  an  hour,  5.22  inches  in  3  hours,  and  6  inches  in 
5  hours.  Of  the  water  of  ordinary  storms  much  of  it  does  not 
reach  the  streams,  and  that  which  does  reach  them  occupies 
days  and  weeks  in  so  doing.  In  storms  such  as  we  have  been 
speaking  of  it  is  certain  that  if  the  rain  continued  indefinitely 
*  These  figures  are  given  by  Kuichling,  Trans.  Am.  Soc.  C.E.,  vol.  xx. 


I  5  8  RESER  VOIR-DA  MS.     S 1  OR  A  GE-RESER  VOIRS. 

the  water  would  reach  the  stream  at  the  same  rate  as  it  falls 
upon  the  ground.  There  is  reason  to  think  that  this  condition 
is  sometimes  reached  in  the  case  of  sewers  discharging  the 
water  which  falls  upon  roofs  and  pavements,  but  in  the  case  of 
storage-reservoirs  receiving  the  drainage  of  a  large  area  of  the 
natural  ground  there  is  no  reason  to  think  that  the  rain  ever 
falls  long  enough  to  put  the  stream  in  this  condition.  This 
condition  is  approached  more  closely  in  steep  and  rocky  regions 
than  in  level  districts  abounding  in  swamps  and  forests,  and  it 
is  more  closely  approached  in  small  districts  than  in  large  ones. 
This  condition  would  imply  for  a  rainfall  of  2  inches  an  hour 
a  discharge  of  1 300  cubic  feet  per  second  per  square  mile,  a 
rate  of  flow  vastly  in  excess  of  any  authentic  observation.  The 
highest  flow  that  ever  came  under  the  writer's  observation  was 
about  1 50  cubic  feet  per  second  per  square  mile  for  a  district  of 
2O  square  miles. 

A  more  reliable  idea  of  the  greatest  flood  to  be  expected 
may  be  obtained  from  the  flood-marks  which  are  usually  within 
the  recollection  of  old  residents  or  among  the  traditions  of  the 
locality.  These  flood-marks,  supplemented  by  the  necessary 
measurements,  usually  give  the  data  for  computing  with  suffi- 
cient accuracy  the  flow  of  the  stream,  and  the  greatest  flow  of 
the  stream  that  has  occurred  in  a  century  may  safely  be  taken 
as  a  basis  for  determining  the  dimensions  of  the  wasteway. 

The  extent  to  which  the  width  of  the  wasteway  is  affected 
by  the  area  of  the  reservoir  will  appear  from  the  following : 
Suppose  two  reservoirs  of  equal  capacity;  the  one  of  shallow 
depth,  covering  iooo  acres,  the  other  of  great  depth,  covering 
200  acres.  The  areas  are  taken  at  the  level  of  the  wasteway, 
and  extension  of  area  consequent  upon  rise  is  disregarded. 
The  top  of  the  embankment  is  supposed  to  be  5  feet  above  the 
sill  of  the  wasteway.  Suppose  we  find  reason  to  expect,  as  a 
maximum,  10000  cubic  feet  of  water  per  second  continuing  for 
three  hours,  then  subsiding  to  iooo  cubic  feet  per  second  at  the 
end  of  the  sixth  hour.  Assuming  the  water  to  be  at  the  level 
of  the  wasteway  at  the  commencement  of  the  flood,  it  is  mani- 


THE    WA  STEW  AY.  I  59 

fest  that  the  first-named  reservoir  would  take  the  entire  volume 
of  the  flood,  making  no  account  of  the  discharge,  without 
raising  the  water  more  than  4  feet,  and  that  a  wasteway 
capable  of  discharging  1000  cubic  feet  per  second  at  the  latter 
height  would  be  abundant.  On  the  other  hand,  the  2OO-acre 
reservoir  would  not  be  safe  without  a  wasteway  capable  of  dis- 
charging at  the  danger-level,  which  we  will  call  4.5  feet  above 
the  wasteway,  a  quantity  equal  to  the  total  inflow.  This  may 
be  shown  by  a  little  computation.  A  wasteway  discharging 
10  ooo  cubic  feet  per  second  at  a  depth  of  4.5  feet  would  dis- 
charge at  any  other  depth,  h,  10  ooo —  =.  On  this  prin- 

4-5^4-5 

ciple  we  compute  the  discharge  of  such  a  wasteway  for  different 
depths  as  follows: 


0.5  feet 370.4  cu.  ft.  per  sec. 

i.o    "    1047.6       "  " 

i-5    "    I924-5       " 


3.0  feet 5443-3  cu.  ft.  per  sec. 

3-5    "    6859.4       " 

4.0    "    8380.5 

4.5    "    10000.0 


2.0     "      ........  2963.0 

2.5     "      ........  4140.9          " 

We  assume  the  water  to  stand  even  with  the  wasteway  at 
the  commencement  of  the  flood.  The  average  discharge  while 
rising  the  first  half-foot  maybe  taken  as  ^  of  370  =  185.  The 
time  occupied  in  rising  the  first  half-foot  will  be 

4356  ooo 
From  o.  5  to  i  =  —  —  =  469 


1  to  1.5  ..........  :  ...............  512 

i-5  to  2  ...........................  577 

2  tO  2.5  ...........................  '676 

2.5  to  3  ...........................  836 

3  to  3.5  .....  .  .....................  1132 

3-5  to  4  ...........................  1830 

4  to  4.25  ......  ....................  3585 


Total  time 10  061  sec. 

=  2h  47m4is- 


160  RESERVOIR-DAMS.     STORAGE-RESERVOIRS. 

We  thus  have  the  water  4  feet  3  inches  above  the  crest  of 
the  wasteway  before  the  termination  of  the  flood,  and  must 
admit  that  the  wasteway  is  none  too  large. 

It  is  a  very  favorable  condition  when  the  wasteway  can  be 
placed  on  natural  ground  at  a  distance  from  the  embankment. 
Such  situations  are  not  uncommon.  Reservoir-dams  are  always 
placed  where  the  ridges  enclosing  the  valley  approach  closely 
to  one  another.  Not  infrequently  it  occurs  that  a  depression, 
in  one  of  the  ridges  may  be  made  available  for  a  wasteway. 
Cases  even  occur  m  which  the  wasteway  is  in  rock,  while  the 
rock  at  the  dam-site  lies  far  below  the  surface.  Where  the 
conformation  necessitates  placing  the  wasteway  on  the  embank- 
ment it  is  constructed  by  spreading  a  bed  of  masonry  on  the 
exterior  slope  with  two  side  walls  to  limit  its  width.  Whether 
it  should  be  narrow  and  massive  or  broader  and  less  massive 
will  often  be  a  debatable  question.  In  the  former  case,  the 
embankment  must  rise  higher  than  in  the  latter,  which  is 
coupled  with  the  disadvantage  that  in  the  event  of  a  disaster 
from  insufficiency  of  the  wasteway  there  would  be  a  greater 
volume  of  water  set  free  for  mischief  than  in  the  latter  case. 
The  wider  the  wasteway  the  less  occasion  for  massiveness  in 
its  bed.  If  we  suppose  a  wasteway  of  such  width  that  the  water 
never  need  rise  more  than  2  feet  above  its  crest,  there  is  no 
reason  to  doubt  that  a  thickness  of  12  inches  of  the  best  con- 
crete would  be  perfectly  safe.  The  water  in  this  case  would 
take  a  depth  of  about-  16  inches,  after  passing  the  crest,  and  the 
descending  sheet  would  have  .a  thickness  of  not  more  than 
3  inches  after  a  descent  of  30  feet.  It  must  be  remembered  in 
this  case  that  water  running  down  a  smooth  slope  has  no 
power  to  injure  its  bed.  Its  power  for  mischief  is  developed 
by  meeting  with  obstacles,  and  fully  developed  when  its  motion 
is  arrested  at  the  end  of  its  descent.  It  is  also  to  be  remem- 
bered that  water  in  this  case  never  carries  ice  or  floating  bodies, 
and  further  that  the  wasteway,  carrying  water  only  at  rare 
intervals,  is  at  all  other  times  accessible  for  examination  and 
repairs.  The  possibility  of  water  getting  under  the  bed  and 


THE    WASTE  WAY.  l6l 

coming  to  a  pressure  sufficient  to  crack  or  derange  it  is  to  be 
carefully  guarded  against.  Wasteways  are  sometimes  made 
with  a  narrowing  channel  designed  to  maintain  the  depth 
uniform  while  the  velocity  increases.  This  method  concen- 
trates the  entire  energy  of  the  stream  at  its  outfall  upon  a  small 
area,  and  calls  for  massive  vvork  to  resist  the  abrasion. 

Fig.  80  is  a  section  through  the  wasteway  built  on  the 
embankment.  At  the  foot  of  the  slope,  the  ground  is  excavated 
to  the  level  of  2  or  3  feet  below  low  water,  the  excavation 
extending  the  entire  width  of  the  wasteway,  and  the  bottom 
protected  against  the  wash  of  the  same.  This  protection  may 
consist  of  heavy  stone  or  a  bed  of  concrete,  but  the  form  here 
contemplated  is  a  lining  of  timber ;  8-  or  p-inch  square  timbers 
are  laid  down  2  or  3  feet  apart,  and  confined  by  long  iron  rods 
driven  through  them  into  the  ground.  A  flooring  of  3-inch 
plank  is  laid  upon  these  timbers,  and  along  the  up-stream  end 
of  this  platform  the  foot-wall  is  built.  The  "sluices  discharge 
through  this  foot- wall,  which  rises  above  low  water.  The  top 
of  this  wall  forms  the  footing  of  the  wasteway,  which  consists 
of  a  concrete  bed  bounded  by  two  side  walls  running  up  the 
slope.  The  toe  of  this  wasteway  might  advantageously  take  a 
form  to  give  the  discharge  an  upward  turn,  as  such  a  thin  sheet 
leaping  into  the  air  would  break  into  spray  and  fall  harmlessly. 
Floating  bodies  are  not  here  to  be  apprehended.  Outside  the 
wasteway  the  earth  rises  to  the  top  of  the  side  walls.  The  side 
walls  continue  to  the  inner  slope  of  the  embankment.  The 
floor  connects  with  the  puddle-wall  or  the  face-puddle,  and  if 
there  is  no  puddle,  it  should  terminate  in  a  wall  of  masonry  sunk 
4  or  5  feet  into  the  crown  of  the  embankment. 

In  constructing  a  reservoir-dam  commanding  a  large 
drainage-area,  the  occurrence  of  a  flood  during  the  process  of 
construction  is  a  contingency  not  to  be  overlooked.  The  dis- 
charge of  the  outlet  even  under  full  head  is  but  a  small  frac- 
tion of  what  might  be  expected  in  a  flood.  A  dam  of  masonry 
resting  on  rock  can  be  overflowed  at  any  stage  of  its  construc- 
tion without  danger,  but  the  passage  of  water  over  an 


1 62  RESER  VOIR  D  A  MS.     S  TOR  A  GE-RESER  VOIRS. 

unprotected   embankment  would  inevitably  cause  its  destruc- 
tion. 

Fig.  8 1  indicates  a  mode  of  constructing  an  embankment 
so  as  to  be  prepared  for  the  occurrence  of  a  flood  at  any  stage 
of  its  progress.  The  toe  of  the  embankment  is  constructed  as 
shown  at  Fig.  80.  As  fast  as  the  embankment  rises,  timbers 


FIG.  80. 


or  sleepers  about  9  inches  square  are  imbedded  in  the  outer 
slope,  and  confined  by  long  iron  rods  driven  into  the  embank- 
ment. The  timbers  extend  the  width  of  the  work,  shown  by 
Fig.  81,  and  the  wider  this  is,  the  better  for  the  purpose. 


FIG.  81. 

The  sleepers  are  covered  with  a  flooring  of  2-  or  3-inch  plank, 
in  lengths  only  sufficient  to  reach  from  one  to  another.  This 
flooring  is  terminated  by  side  walls  of  plank,  sustained  by 
uprights  mortised  into  the  sleepers  and  braced  therefrom,  the 
sleepers  being  continued  beyond  the  side  walls  for  that  purpose. 


THE    WASTEWAY. 


163 


The  embankment  is  kept  level  from  end  to  end  during  con- 
struction. 

On  the  occurrence  of  rains  sucn  as  to  warrant  the  expecta- 
tion of  a  flood,  construction  work  is  suspended.  A  crew  of 
men  proceed  to  lay  down  timbers  1,2,  and  3  on  the  top  of  the 
embankment,  and  cover  them  with  plank  joined  to  the  com- 
pleted planking  as  shown.  A  second  party  drives  a  row  of 
tongued  and  grooved  spiling,  2  or  3  feet  deep,  against  the 
up  stream  face  of  timber  No.  I,  sawing  them  off  and  spiking 
them  to  the  timber.  A  third  lays  down  the  timbers  4,  5,  and 
6  from  the  wasteway  to  end  of  embankment.  A  fourth  drives 
the  row  of  3-  or  4-inch  spiling  on  that  part  of  the  work,  Fig. 
8ia.  A  fifth  puts  in  the  bracing.  The  ordinary  construction 


FIG.  8r«. 

gang  furnishes  laborers  sufficient  for  this  emergency.  Car- 
penters are  summoned  as  soon  as  it  arises,  at  prices  that  will 
command  their  services.  All  the  timber  required  is  kept  in 
readiness  from  the  beginning,  together  with  all  necessary  tools 
and  a  supply  of  rubber  coats  and  boots,  so  that  men  may  be 
induced  to  work  without  regard  to  weather  or  working  hours. 

This  temporary  work  may  serve  the  purpose  of  a  wasteway 
for  several  years  after  completion  of  the  reservoir,  but  must  be 
replaced  by  masonry  as  soon  as  decay  appears. 


CHAPTER   VIII. 
ROCK-FILL    DAMS. 

IN  the  mining  operations  which  commenced  in  California 
some  fifty  years  ago,  and,  later,  in  the  necessity  for  irrigation 
which  arose  in  this  and  neighboring  regions,  many  projects  for 
collecting,  storing,  and  conducting  water  on  a  large  scale  have 
been  executed.  These  were  at  first  controlled  by  men  of  very 
limited  scientific  knowledge,  though  of  great  energy  and  natural 
sagacity.  The  traditions  of  the  engineering  profession  have 
been  largely  disregarded,  and  though  many  failures  have  been 
incurred  and  great  losses  sustained,  the  result  is  that  works 
have  been  executed  and  methods  of  construction  adopted,  and 
have  stood  the  test  of  time,  which  no  engineer  with  a  reputation 
to  maintain  would  have  dared  to  recommend,  and  which  in  the 
older  sections  of  the  country  would  have  appeared  too  bold  and 
hazardous  for  the  investment  of  money  even  if  so  recommended. 
Among  these  works  are  dams  often  more  than  a  hundred  feet 
in  height,  built  of  loose  rock  and  sustaining  an  impervious  skin 
to  prevent  the  passage  of  water.  These  dams  occupy  deep 
ravines  worn  in  the  rock  formation,  which  are  usually  dry  for 
several  months  in  the  year,  so  that  there  is  usually  time  to 
start  the  work,  to  lay  the  sluices,  and  to  raise  the  bank  high 
enough  to  create  a  head  capable  of  passing  a  good  flow  of 
water  before  the  stream  commences  to  flow.  Of  course  the 
sluices  cannot  be  made  capable  of  carrying  off  the  greatest  flow 
of  the  stream,  and  such  a  work  while  under  construction  is,  to 
a  greater  or  less  extent,  at  the  mercy  of  a  flood,  a  risk  which 
has  to  be  accepted  or  provided  for,  though  it  is  to  be  observed 

164 


ROCK-FILL   DAMS.  l6$ 

that  this  work  is  susceptible  of  much  more  rapid  construction 
than  the  ordinary  earth  embankment. 

The  wasteway  of  such  a  dam  is  usually  cut  in  the  escarp- 
ment of  the  ravine,  passing  around  the  end  of  the  dam,  a  few 
feet  below  the  level  of  high  water.  Fig.  82,*  a,  b,  c,  d,  shows 
a  rock-fill  dam  recently  constructed  at  Escondido,  San  Diego 
County,  California,  on  the  Von  Segern  branch  of  San  Eligo 
Creek.  The  drainage-area  of  this  creek  was  very  small,  not 
over  8  square  miles.  The  main  supply  of  the  reservoir  was 
obtained  from  the  San  Luis  Rey  River  by  means  of  a  tunnel 
through  the  intervening  ridge.  The  work  was  thus  free  from 
serious  risk  of  damage  from  high  water  during  its  construction. 
The  dam  is  76  feet  high;  380  feet  long  on  top,  100  feet  on 
bottom ;  140  feet  thick  at  bottom,  10  at  top.  The  slopes  of  the 
dam  are  £  to  I  on  the  water-face,  I  to  I  on  the  down-stream 
face  for  the  upper  half,  I J  to  I  for  the  lower  half.  The  front 
face  to  a  thickness  of  1 5  feet  at  bottom  and  5  feet  at  top  was 
laid  by  hand.  The  remainder  consists  of  loose  angular  granite 
blocks  up  to  4  tons  weight,  dumped-  from  cars  and  handled  to 
some  extent  by  derricks.  Tracks  for  tram-cars  were  carried 
across  the  dam  on  trestles,  which  were  lengthened  upward  as 
the  dam  rose,  leaving  the  posts  imbedded  in  the  rockwork. 
Along  the  up-stream  face  a  trench  was  excavated  3  to  1 2  feet 
deep,  5  feet  wide,  into  the  bed-rock,  and  filled  with  rubble 
masonry  laid  in  Portland  cement,  forming  a  footing  to  connect 
the  plank  facing  with  the  bottom  and  sides  of  the  ravine. 
Timbers  6x6  inches  were  imbedded  to  a  depth  of  4  inches  in 
the  slanting  face  of  the  dam,  running  up  and  down,  5  feet 
apart.  To  these  timbers  plank  are  spiked  to  form  the  water- 
tight skin  of  the  dam.  The  plank  are  3  inches  thick  on  the 
lower  third,  2  for  the  middle,  and  i£  for  the  upper.  This 
plank  facing  is  carried  up  to  a  height  of  3  feet  above  the  top 
of  the  dam,  9  feet  above  the  sole  of  the  wasteway.  The  space 
between  the  planking  and  the  wall  is  packed  with  concrete. 
The  sluice  is  a  24-inch  vitrified  sewer-pipe  imbedded  in  con- 
*  Eighteenth  Annual  Report  U.  S.  Geol.  Survey,  Part  IV,  PI.  XLIX. 


KESER  V OIR-DA  MS. 


ROCK- FILL   DAMS.  1 67 

crete.  It  is  closed  by  a  sliding  gate  which  is  operated  by  a 
rod  running  down  the  inclined  face  of  the  dam.  Fig.  82  is  a 
section  of  the  ravine  and  wasteway,  8za  plan  of  same,  82^ 
section  of  dam  through  sluice.  82^  shows  plank  facing,  82^? 
rubble  trench  and  footing.  This  dam  has  been  in  use  since 

1895- 

Figs.  83,  a,  b,  c,  d,  represent  a  dam  of  a  still  more  startling 
character,  the  impervious  skin  consisting  of  a  steel  diaphragm 
extending  entirely  across  the  valley  .from  top  to  bottom.  This 
dam  was  under  construction  at  last  accounts  and  is  presumed 
now  to  be  completed.  The  details  are  obtained  from  the 
same  source  as  in  the  former  case,*  and  we  cannot  do  better 
than  use  the  language  of  the  Report : 

' '  One  of  the  most  interesting  and  remarkable  dams  now 
under  construction  is  located  20  miles  southeast  of  San  Diego, 
California,  about  10  miles  back  from  the  coast,  on  Otay  Creek. 
The  stream  here  cuts  through  the  great  porphyry  dike  which 
traverses  San  Diego  County  from  north  to  south  nearly  parallel 
to  the  coast-line.  The  dike  is  several  miles  in  width,  and  is 
crossed  and  cut  into  by  all  the  streams  of  the  county  that  reach 
the  ocean,  affording  sites  for  the^Sweetwater  and  the  La  Mesa 
dams,  already  built,  and  others  farther  north  that  are  projected. 
The  dam  is  being  built  to  store  water  for  irrigation  and  domes- 
tic supply  on  Coronado  Beach  and  the  regions  south  and  east 
of  the  head  of  the  Bay  of  San  Diego.  Its  ultimate  height  above 
the  stream-bed  is  to  be  130  feet,  and  it  will  be  completed  early 
in  1897.  It  is  a  simple  embankment  of  loose  stone,  dumped 
in,  without  any  portion  of  it  being  laid  by  hand  as  a  wall,  and 
depending  for  water-tightness  on  a  central  core  of  steel  plates 
riveted  together  after  the  fashion  of  a  large  tank,  forming  a 
web-plate  across  the  canyon  from  wall  to  wall,  filling  the  entire 
cross-section.  It  was  originally  intended  to  build  a  masonry 
dam  at  this  place,  and  a  foundation  was  laid  for  that  purpose, 
62  feet  thick  at  the  base.  This  masonry  reaches  down  to  a 
depth  of  31.4  feet  below  zero  contour,  into  an  irregular  '  pot- 
*  Eighteenth  Annual  Report  U.  S.  Geological  Survey,  Part  IV,  p.  637. 


168 


OIR-DA  MS. 


CROSS-SECTION  OF  DAM 


TUNNEL  SECTION 
0  4  Ft. 


234567 


PROFILE  OF  OUTLET  OF  TUNNEL  ' 


TUNNEL  SECTION 


ROCK-FILL   DAMS,  169 

hole  '  excavated  in  the  softer  portion  of  the  bed-rock  under 
the  stream-bed,  and  it  was  carried  up  to  8.6  feet  above  zero 
before  the  plan  was  changed,  its  length  being  about  100  feet 
at  this  level.  The  up-stream  side  of  this  masonry  was  built 
as  an  obtuse  angle  of  about  164°,  and  on  this  foundation  and 
6  feet  back  from  the  face,  the  line  of  steel*  plates  was  begun, 
following  the  same  central  angle  as  the  masonry  foundation. 
The  plates  were  5  feet  wide  and  17.5  feet  long,  and  the  three 
bottom  courses  were  0.33  inch  thick.  From  28  to  50  feet 
height  they  are  one-fourth  inch  thick,  and  above  50  feet  they 
are  8  feet  wide  and  20  feet  long.  The  plates  were  riveted  in 
position,  chipped  and  calked,  and  afterwards  smeared  with  hot 
asphaltum  and  covered  both  sides  with  burlap  saturated  in  the 
same  material. 

"Starting  at  the  foundation,  a  rubble-masonry  wall  was 
built  up  each  side  of  the  plates,  6  feet  thick  at  bottom,  batter- 
ing up  on  both  sides  in  a  height  of  8  feet  to  I  foot  which  thick- 
ness was  continued  to  the  top.  This  masonry  was  somewhat  in 
the  nature  of  concrete,  as  it  was  rammed  in  between  a  mould  of 
p  anks  and  boards  placed  on  each  side  of  the  plate,  with  a  large 
rock,  often  the  full  thickness  of  the  wall,  imbedded  in  the 
mortar.  Its  function  was  evidently  to  stiffen  and  steady  the 
web-plate  and  protect  it  from  injury  from  the  loose  rock  piled 
against  it.  At  the  ends  the  plates  were  carried  into  a  trench 
excavated  into  the  solid  rock,  and  fastened  to  anchor-bolts  set 
into  the  rock,  the  masonry  being  expanded  to  a  greater  width 
for  a  few  feet  at  the  sides.  The  depth  and  width  of  the  trench 
were  quite  irregular,  depending  upon  the  direction  and  position 
of  seams  in  the  rock. 

"The  expansion  of  the  plates,  after  they  were  riveted 
together,  gave  them  a  very  irregular  alignment,  and  before  they 
had  reached  the  5O-foot  level  the  angle  in  plan  had  almost 
entirely  disappeared  and  the  sheet  was  in  a  practically  straight, 
but  wavy,  line  from  side  to  side.  In  order  to  straighten  up  in 
this  way  the  sheet  must  be  inclined  from  the  vertical  at  some 
points,  and  this  inclination  may  be  as  great  as  7  feet  in  the 


I/O  /      RESERVOIR-DAMS. 

total  height.  The  possible  effect  of  the  settlement  of  the  great 
mass  of  stone  in  the  rupturing  of  the  plate  when  the  reservoir 
is  filled  and  one-half  the  wall  is  enveloped  in  water  must  be 
regarded -with  some  measure  of  concern.  The  uncertainty  as 
to  the  strains  set  up  in  the  central  core  and  the  impossibility  of 
calculating  them  in-advance  must  be  urged  against  this  innova- 
tion in  dam-construction,  although  the  experiment  will  be 
watched  with  genuine  interest  by  the  engineering  profession. 

' '  The  stone  was  quarried  immediately  below  the  dam  on 
the  right  bank,  and  was  transported  by  means  of  a  Lidgerwood 
cableway,  the  cable  having  a  diameter  of  2^  inches  and  a  span 
of  948  feet  between  towers,  crossing  the  canyon  at  an  angle 
of  about  60°  with  the  axis  of  the  dam.  The  head  tower  was 
100  feet  high,  the  tail  tower  down-stream  was  40  feet  in  height, 
and  a  direct  line  between  them  crossed  the  site  of  the  dam  260 
feet  above  the  bed  of  the  -stream.  The  cableway  has  a  maxi- 
mum capacity  for  carrying  10  tons  weight,  under  which  load 
the  deflection  is  88  feet.  It  has  therefore  not  been  necessary 
to  move  the  cable  during  construction,  from  the  time  of  its 
erection  in  1894  till  the  completion  of  the  dam.  The  distribu- 
tion of  the  rock  either  side  of  the  line  of  the  cable  has  been 
'  made  by  powerful  derricks,  and  latterly  by  a  small  auxiliary 
cable  stretched  parallel  with  the  line  of  the  dam  and  anchored 
to  cars  movable  on  parallel  tracks  on  either  side  of  the  valley. 

"...  The  total  volume  of  the  dam  to  the  I  3O-foot  line 
with  top  width  of  20  feet  and  side  slopes  of  I  to  I  on  each  side 
is  approximately  140  ooo  cubic  yards.  .  .  .  The  only  outlet 
to  the  reservoir  has  been  made  by  means  of  a  tunnel,  1 1 50  feet 
long,  through  a  gap  in  the  ridge  1000  feet  west  of  the  dam. 
The  bottom  of  the  tunnel  is  at  the  5O-foot  level.  The  material 
encountered  in  the  tunnel  was  hard-pan  and  cemented  gravel, 
bone-dry.  For  500  feet  from  the  inner  heading  it  was  lined 
with  concrete  to  a  clear  circular  diameter  of  5  feet,  the  concrete 
being  from  12  to  18  inches  thick  and  plastered  with  cement 
mortar.  At  the  end  of  this  section  a  shaft  104  feet  in  depth 
reaches  to  the  surface,  to  admit  of  the  operation  of  a  gate  across 


ROCK-FILL  DAMS.  I/I 

the  conduit.  Outside  of  the  shaft  a  48-inch  steel  pipe  is  laid 
to  the  outside ;  this  is  surrounded  with  I  foot  or  more  of  Port- 
land-cement concrete,  filling  the  space  between  the  pipe  and 
the  irregular  surface  of  the  tunnel,  with  collars  of  concrete 
every  25  feet,  and  I  to  2  feet  deep  all  around  the  pipe.  There 
are  no  pipes  or  openings  of  any  sort  through  the  dam. 

' '  The  wasteway  is  to  be  located  on  the  left  bank,  some 
hundreds  of  feet  away  from  the  dam,  and  discharging  at  a  safe 
distance  below  the  foot  of  the  embankment.  .  .  . 

' '  The  watershed  of  Otay  Creek  above  the  reservoir  is  about 
100  square  miles  in  area;  but  as  its  average  altitude  is  not  over 
i  500  feet,  the  precipitation  is  light  and  the  run-off  insufficient 
to  fill  the  reservoir  except  in  occasional  years.  In  dry  seasons 
there  is  no  flow  whatever.  To  make  up  for  this  shortage  and 
to  fill  the  reservoir  regularly  the  company  is  planning  to  divert 
the  water  from  Cottonwood  Creek,  a  larger  and  more  reliable 
stream  on  the  south  and  lying  next  to  Mexican  territory,  by  a 
conduit  1 2  miles  in  length  from  the  diverting-weir,  at  what  is 
known  as  the  Barrett  dam,  to  Dulzura  Pass,  where  the  water 
will  drop  over  into  the  Otay  drainage. ' ' 

A  general  idea  of  the  dam  is  shown  by  Fig.  83,  which  is  a 
plan  of  dam  showing  contours  of  ravine;  830,  a  condensed 
cross-section  of  ravine ;  83^,  section  of  dam ;  8 3^,  tunnel  pipe; 
and  83^,  section  of  ridge  showing  tunnel. 

Fig.  84  is  a  cross-section  of  a  rock-fill  dam  built  across  the 
Rio  Pecos  in  1889-90,  near  the  town  of  Eddy,  New  Mexico. 


FIG.  84. 


The  peculiarity  of  this  construction  is  that  it  depends  for  water- 
tightness  upon  a  bank  of  earth.      The  rock-fill  is  48  feet  high 


1 72  KESEK  VOIR-DA  MS. 

in  the  middle,  with  a  down-stream  slope  of  i^  to  I  and  an 
up-stream  slope  of  i  to  I,  being  faced  with  a  dry  retaining, 
wall.  It  has  a  top  width  of  10  feet.  Against  the  rock-fill  on 
the  up-stream  side  rests  a  bank  of  earth  with  a  slope  of  3^ 
to  i,  and  a  top  width  of  16  feet,  making  the  total  top  width  of 
the  dam  20  feet.  The  Pecos  River  at  this  point  has  a  flood- 
volume  of  over  40000  cubic  feet  per  second  and  has  been 
observed  as  low  as  200.  In  1 893  a  flood  occurred  in  excess 
of  the  capacity  of  the  wasteway.  The  water  ran  over  the  crest 
of  the  dam  and  speedily  destroyed  it.  It  was  immediately 
rebuilt,  raised  5  feet  higher,  and  provided  with  additional 
wasteway  capacity. 

Embankments  made  by  Sluicing. — Another  method  of 
constructing  reservoir-embankments  has  been  developed  ex- 
clusively in  California  in  the  course  of  operations  incident  to 
placer-mining,  especially  to  the  sluicing  down  and  washing 
away  of  hills  and  banks  of  auriferous  gravel.  The  method 
consists  in  sluicing  the  material  of  the  dam  into  position  by  the 
aid  of  running  water.  La  Mesa  dam,  near  San  Diego,  Cal., 
holding  a  head  of  60  feet  of  water,  was  constructed  in  this 
manner.  As  a  clear  exposition  of  this  method,  I  quote  from 
the  above  report  a  description  of  the  construction  of  a  dam  at 
Tyler,*  Texas: 

' '  The  experience  which  led  up  to  the  construction  of  the 
La  Mesa  dam  and  the  planning  of  the  other  structures  described 
was  obtained  by  Mr.  Howells  by  the  building  of  a  dam  in 
Tyler,  Texas,  by  the  same  method  in  1894,  which  developed 
so  many  interesting  features  that  a  brief  account  of  it  will  here 
be  given,  as  it  has  never  been  described  in  print  before.  The 
dam  is  575  feet  long,  32  feet  high,  and  contains  24  ooo  cubic 
yards,  the  inner  slopes  being  3  to  I ,  and  the  outer  2  to  i ,  with 
a  4-foot  berm  on  the  inside  10  feet  below  the  top.  This 
impounds  1770  acre-feet, t  covering  177  acres.  The  maximum 
depth  is  26  feet.  All  the  material  used  in  the  dam  was  sluiced 

*  Eighteenth  Annual  Report,  etc.,  p.  654. 
f  The  acre-foot  in  an  acre  one  foot  deep. 


EMBANKMENTS  MADE  BY  SLUICING.  1/3 

In  from  a  neighboring  hill  at  a  cost  of  4!  cents  per  cubic  yard, 
including  the  plant  and  all  appurtenances  of  the  reservoir. 
The  water  was  pumped  through  a  6-inch  pipe  from  the  old  city 
pumping-station  on  the  opposite  side  of  the  valley  from  the  hill 
which  supplied  the  materials.  This  hill  is  150  feet  high,  and 
the  pipe  terminated  about  half-way  up  from  its  base,  where  a 
common  fire-hydrant  was  placed,  to  which  was  attached  an 
ordinary  2^-inch  hose,  with  a  nozzle  of  i£  inches  diameter. 
From  this  nozzle  a  stream  was  directed  against  the  face  of  the 
hill  under  a  pressure  limited  to  100  pounds  per  square  inch. 
The  washing  was  carried  rapidly  into  the  hill  on  a  3  per  cent 
grade,  which  soon  gave  a  working-face  of  10  feet  or  more, 
increasing  gradually  to  36  feet  in  vertical  height.  By  main- 
taining the  jet  at  the  foot  of  the  cliff  it  was  undermined  as 
rapidly  as  it  could  be  carried  away  by  the  water. 

4  '  The  material  found  in  the  hill  consisted  of  a  soft,  friable 
sandstone,  infiltrated  with  ochre  of  varying  shades — yellow, 
trown,  and  red — alternating  with  clay  and  sand,  the  whole 
overlain  by  a  sandy  loam  soil  from  2  to  6  feet  deep.  Experi- 
ment and  observation  led  to  the  conclusion  that  65  per  cent  of 
the  entire  mass  washed  into  the  dam  was  sand  and  35  per  cent 
clay. 

4 '  In  beginning  the  work  a  trench  4  feet  wide  was  excavated 
through  the  surface  soil,  down  into  the  clay  subsoil,  a  depth  of 
several  feet,  and  this  was  first  filled  with  selected  puddle-clay 
sluiced  in  by  the  stream.  Then  the  form  of  the  dam  was  out- 
lined by  throwing  up  low  sand-ridges  at  the  slope  lines,  which 
were  maintained,  as  the  dam  rose  in  height,  by  men  with  hoes. 
A  pond  of  water  was  thus  maintained  over  the  top  of  the  dam, 
the  water  being  drawn  off  from  time  to  time,  either  into  the 
reservoir  or  outside,  as  preferred.  The  material  was  trans- 
ported from  the  bank  in  a  13 -inch  sheet-iron  pipe,  with  loose 
jokits,  stovepipe  fashion,  extending  from  near  the  face  of  the 
bluff,  where  the  jet  was  operating,  across  the  centre  line  of  the 
dam.  These  were  so  arranged  as  to  be  easily  uncoupled  at 
any  point,  so  as  to  direct  the  deposit  where  -required  to  build 


1 74  AESER  VOIR-DAMS. 

up  the  embankment  uniformly.  It  was  found  that  the  quantity 
of  solids  brought  down  by  the  water  varied  from  1 8  per  cent 
in  solid  clay  to  30  per  cent  in  sand.  Sharp  sand  does  not  flow 
as  readily  as  rounded  sand  or  gravel,  and  is  improved  in 
delivery  by  an  admixture  of  clay  and  stones.  The  entire 
amount  of  water  pumped,  computed  by  the  percentages  of 
solids  given,  must  have  been  less  than  20000000  gallons. 
The  limitation  of  the  nozzle-pressure  to  100  pounds  per  square 
inch  is  thought  to  have  restricted  the  duty  of  the  water  used  to 
considerably  less  than  might  have  been  accomplished  with 
higher  pressure.  .  The  entire  cost  of  the  dam  with  all  its  acces- 
sories is  given  at  $1140,  which  must  be  regarded  as  a  marvel 
of  cheapness,  and  gives  an  average  cost  per  acre-foot  of 
storage-capacity  of  reservoir  formed  by  it  of  65  cents.  The 
dam  is  reported  to  have  no  apparent  defects  and  gives  satisfac- 
tory service.  Mr.  L.  W.  Wells  was  engineer  and  foreman  in 
charge  of  the  work,  from  whose  memoranda,  furnished  by 
Howells,  consulting  engineer,  the  foregoing  description  has 
been  compiled. ' ' 

It  is  asserted  that  embankments  built  in  this  manner  are 
firmer,  less  liable  to  settlement,  and  more  impervious  than  those 
built  in  the  ordinary  manner.  It  is  well  known  that  the  action 
of  water-  in  excavating,  moving,  and  depositing  earth  has 
recently  received  very  extended  application  in  dredging.  It 
has  also  been  applied  with  great  success  in  railroad  work, 
many  embankments  having  been  recently  put  in  on  the 
Northern  Pacific  and  Canada  Pacific  roads,  by  sluicing  at  a  cost 
as  low  as  5  cents  a  cubic  yard. 


CHAPTER   IX. 
RESERVOIR-DAMS   OF   MASONRY. 

MASONRY  dams  for  impounding  water  differ  from  those 
designed  to  create  a  head  for  water-power  in  two  ways:  i.  As 
to  the  sluices  for  discharging  the  water,  which  are  not  an 
essential  feature  of  the  latter  class.  2.  In  adaptation  to  the 
discharge  of  flood-waters,  which  generally  forms  no  important 
modification  of  the  former,  this  class  usually  commanding  a 
comparatively  limited  drainage-area.  This  difference  becomes 
more  marked  as  the  height  increases,  and,  at  the  limit  of 
height,  the  latter  class  usually  has  dimensions  greatly  in  excess 
of  what  the  pressure  would  call  for,  and  its  form  is  controlled 
mainly  by  the  necessity  of  protecting  itself  from  the  action  of 
water  in  motion,  while  the  former  is  designed  mainly  with 
reference  to  the  pressure.  In  other  words,  the  latter  conforms 
in  shape  and  dimensions  to  the  dynamic  action  of  water,  the 
former  to  its  static  action.  The  limit  of  height  in  a  water- 
power  dam  may  with  limited  exceptions  be  taken  at  40  feet, 
while  storage-dams  rise  to  a  height  of  1 50  and  200.  The 
Quaker  Bridge  Dam  now  under  construction,  pertaining  to  the 
New  York  water-works,  is  intended  to  reach  a  height  of  265 
feet  above  the  rock. 

No  instance  of  the  failure  of  a  high  masonry  dam  from  the 
crushing  of  the  stone  has  come  to  the  writer's  knowledge. 
Such  dams  have  failed,  but  the  failure  was  due  to  other  causes. 
Engineers  therefore  have  no  experimental  light  to  guide  them 
in  this  class  of  structures,  and  so  far  as  the  true  principles  of 
construction  are  concerned  are  groping  in  the  dark.  The 
danger  of  failure,  like  all  other  dangers  encountered  in  the  dark, 

175 


176  RESERVOIR-DAMS. 

is  avoided  by  giving  it  a  wide  berth.  Engineers  know  that  the 
application  of  certain  rules  will  insure  a  safe  structure.  To 
what  extent  the  dimensions  so  ascertained  might  be  diminished 
without  passing  the  limits  of  safety  they  do  not  know,  though 
they  generally  feel  that  such  dimensions  are  excessive.  Even 
on  the  Pacific  slope,  except  in  some  of  the  curved  dams  we  do 
not  find  the  same  boldness  in  dams  of  masonry  as  appears  in 
other  types.  So  disastrous  are  the  consequences  of  failure  that 
suggestions  of  diminished  massiveness  backed  by  the  ablest 
opinions  would  not  be  likely  to  find  favor  with  those  who  have 
the  responsibility  for  such  structures. 

One  of  the  most  important  recent  works  of  the  kind  under 
discussion  is  the  Quaker  Bridge  Dam*  already  alluded  to. 
Engineers  of  eminence  were  employed  on  the  preliminary 
investigations.  They  discussed  the  subject  with  great  thorough- 
ness, and  their  reports  must  be  held  to  embody  the  best  modern 
practice  in  this  branch  of  construction.  Among  the  rules  and 
dicta  adopted  in  these  discussions  are  the  following : 

1 .  Although  the  work  is  intended  to  be  laid  throughout  in 
Portland-cement  mortar,  tensile  strength  is  ignored  in  all  cal- 
culations relative  to  the  masonry. 

2.  Compressive  strains  are  limited  to  15  tons  per  square 
foot. 

3.  The  resultant  of  the  forces  upon   any  horizontal  joint 
must  fall  within  the  middle  third  of  the  joint. 

Let  us  endeavor  to  discover  the  rational  basis  of  these  rules. 

i.  As  to  Tensile  Strength. — It  is  customary  on  all  impor- 
tant works  to  test  the  tensile  strength  of  cement.  This  opera- 
tion is  regarded  as  a  necessary  detail  of  the  work.  It  is 
conducted  by  skilful  assistants,  the  results  carefully  recorded 
and  tabulated.  The  introduction  of  any  large  quantity  of 
worthless  or  inferior  cement  is  not  an  admissible  supposition, 
except  as  the  result  of  wilful  fraud.  In  testing  established 
brands  of  cement  it  is  no  uncommon  thing  to  find  in  500  con- 

*  Report   of    the   Aqueduct    Commission,    Quaker    Bridge    Dam,    1889. 
New  York. 


MASONRY  DAMS.  1 77 

secutive  tests  not  one  sample  differing  by  25  per  cent  from  the 
average.  It  may  be  assumed  that  an  average  strength  of  400 
pounds  per  square  inch  in  Portland-cement  mortar  mixed  2  to 
i  is  attainable  after  two  years'  exposure.  Strength  of  masonry, 
however,  depends  upon  the  adhesion  of  mortar  to  stone  as 
much  as  upon  its  cohesion.  On  this  point  we  have  some  100 
tests  recently  made  at  the  St.  Mary's  Lock,  on  the  strength  of 
concrete  beams.  These  were  made  not  wholly  as  tests  of 
strength,  but  to  test  many  other  points  of  interest.  All  the 
results  were  consistent  and  free  from  anomaly,  and  a  fair 
deduction  from  them  is  that  a  strength  of  400  pounds  per 
square  inch  is  attainable  in  concrete  and  rubble  masonry  with 
mortar  of  Portland  cement  mixed  2  to  I  after  two  years' 
exposure. 

As  to  the  assumption  that  no  reliance  can  be  placed  upon 
the  tensile  strength  of  masonry  in  a  dam.  Suppose  a  high 
dam  so  constructed  as  to  call  for  tensile  strength  to  the  extent 
of  100  pounds  per  square  inch  on  the  up-stream  side.  Make 
the  extreme  supposition  that  one  barrel  of  the  cement  in  every 
ten  is  worthless,  the  good  cement  having  an  average  strength  of 
400.  It  is  manifest  that  entire  lack  of  strength  in  a  few  square 
yards  of  horizontal  joint  would  have  no  effect.  To  endanger 
the  dam  we  must  assume  at  least  100  square  yards  of  some 
horizontal  joint  devoid  of  tensile  strength.  As  such  work  is 
usually  laid  up  in  layers  some  3  feet  thick,  and  should  contain 
at  least  a  half-barrel  of  cement  to  a  cubic  yard  of  masonry,  this 
supposition  would  imply  that  fifty  barrels  of  the  worthless 
cement  have  come  together  in  some  part  of  the  dam.  The 
slightest  consideration  will  show  that  such  an  event,  except  as 
the  result  of  fraud,  is  too  remote  to  be  considered.  To  speak 
mathematically,  its  probability  is  represented  by  a  fraction  of 
which  the  numerator  is  unity  and  its  denominator  is  the  fiftieth 
po\ver  of  10 — for  all  human  purposes  an  impossibility. 

No  distinction  is  more  important  in  engineering  than  that 
between  a  theoretical  possibility  and  a  degree  of  probability 
entitled  to  practical  consideration.  It  is  within  the  bounds  of 


178  KESEX  V OIK-DA  MS 

possibility  for  any  important  building  to  be  struck  by  a  meteoric 
body  from  the  planetary  spaces.  That  event  is,  however,  not 
sufficiently  probable  to  warrant  any  special  modification  in  the 
design  of  the  building. 

In  like  manner,  the  supposition  that  the  strength  of  any 
continuous  portion  of  the  work  calling  for  50  barrels  of  cement 
could  be  as  low  as  200  pounds  per  square  inch  would  imply 
that  25  barrels  of  worthless  cement  had  found  its  way  into  that 
portion.  Excluding  the  idea  of  wilful  fraud,  such  an  event  is 
too  improbable  to  be  considered.  Nevertheless,  among  the 
possibilities  which  must  enter  into  such  calculations,  wilful  fraud, 
especially  in  contract  work,  cannot  be  wholly  excluded.  A 
sudden  frost,  also,  followed  by  a  thaw  may  destroy  the  tenacity 
of  the  freshly  laid  mortar  on  a  considerable  area  of  the  work. 
It  would  be  impossible,  however,  to  adopt  dimensions  liberal 
enough  to  cover  all  possible  results  of  fraud  and  negligence. 

2.  As  to  the  Compressive  Strength  of  Stone.  — The  crushing 
of  a  solid  body  by  a  force  uniformly  applied  on  all  its  sides  is 
not  possible  or  conceivable.  We  might,  for  instance,  conceive 
a  block  of  stone  enclosed  in  the  cylinder  of  a  hydraulic  press 
and  surrounded  by  water  under  a  pressure  of  100000  pounds 
per  square  inch  without  suffering  the  slightest  injury,  while  the 
same  block  exposed  to  a  pressure  of  10000  pounds  per  square 
inch  on  two  of  its  opposite  faces  would  be  crushed  to  fragments. 
In  this  case  the  compressive  force  resolves  itself  into  compo- 
nents which  overcome  the  tensile  and  shearing  strength  of  *the 
material.  The  crushing  of  a  stone  imbedded  in  mortar  and 
located  in  the  interior  of  a  wall  is  not  to  be  apprehended, 
neither  is  that  of  the  mortar  itself  in  the  joints  of  the  stones. 
It  is  only  the  exterior  stones  which  are  liable  to  fail  from  this 
action.  Nevertheless  the  crushing  of  the  exterior  stone  leaves 
the  adjacent  stones  exposed  to  the  same  danger  in  greater 
measure,  and  the  structure  is  destroyed  in  detail. 

In  dealing  with  bridges  and  similar  structures,  where  the 
failure  of  a  single  piece  would  imperil  the  whole  work,  wide 
margins  of  safety  are  usually  allowed.  The  destruction  of  an 


MASONRY  DAMS.  1/9 

important  bridge  might  result  from  the  failure  of  a  single  bar; 
and  inasmuch  as,  in  a  great  number  of  pieces,  a  defective  one 
will  sometimes  occur,  common  prudence  requires  that  no  pie,ce 
should  be  strained  beyond  a  fourth  or  fifth  part  of  its  presum- 
able strength.  In  dealing  with  large  masses  of  masonry, 
however,  where  failure  would  imply  the  simultaneous  yielding 
of  at  least  a  hundred  contiguous  stones,  it  is  manifest  that  the 
necessity  for  a  wide  margin  of  security  does  not  rest  upon  the 
same  rational  basis.  In  this  case,  as  in  the  case  of  tensile 
strain,  we  must  inquire  what  probability  there  is  of  such  a  simul- 
taneous yielding.  Suppose  that  tests  sufficiently  numerous  and 
complete  show  that  we  may  assume  nine  stones  out  of  every  ten 
to  have  a  strength  of  5000  pounds  per  square  inch,  and  make 
the  extravagant  supposition  that  every  tenth  stone  is  worthless. 
It  is  obvious  that  this  supposition  would  make  the  stone  entirely 
inapplicable  to  a  structure  whose  safety  depended  upon  a  single 
stone.  Yet  it  would  affect  the  value  of  the  stone  to  but  a 
comparatively  slight  extent  in  a  massive  dam.  The  probability 
of -a  hundred  defective  stones  coming  together  in  such  a  work 
is  too  slight  to  enter  into  any  rational  computation. 

The  most  reliable  tests  of  compressive  strength  made  in 
recent  times  are  those  of  General  Q.  A.  Gillmore,  published  in 
the  Report  of  the  Chief  of  Engineers,  U.  S.  A. ,  for  1 87  5 .  This 
embraced  the  principal  varieties  of  stone  used  in  construction 
in  the  United  States.  Also  those  of  Mr.  Thos.  Hudson  Beare, 
reported  in  the  minutes  of  proceedings  of  the  Institution  of  Civil 
Engineers  of  London,  vol.  CXVII.  p.  341  et  seq.,  embracing 
the  series  of  building-stones  in  use  in  Britain.  Mr.  Beare's 
tests  were  made  upon  2^-inch  cubes,  General  Gillmore 's  upon 
2-inch  cubes,  and  he  found  good  reason  to  believe  that  the 
strength  per  square  inch  increases  with  the  size  of  the  piece, 
though  no  testing-machine  has  yet  been  made  massive  enough 
to  crush  a  stone  of  the  size  used  in  practical  construction. 
The  results  are  stated  in  tons  (2240  pounds)  per  square  foot. 

General  Gillmore  found: 


i8o 


££S£A  VO1R-DA  MS. 


99  specimens  of  granite,       highest  1541  tons,  lowest  497 
43  "          "  limestone,        "        1600     "          "       221 

12  "          "  marble,  "        1284     "          "       488 

62  "          "  sandstone,        "        1136     "          "       251 

Mr.  Beare  found: 

88  specimens  of  sandstone,  highest  1090  tons,  lowest  171.5 
1 6  "          "  dolomite,          "         642     "          "       281 

86  "          "  limestone,         "        1075     "          "          58 

49  "          "  granite,  "        144°     "          "       7^6 

It  is  to  be  observed  with  reference  to  both  these  series  of 
tests  that  the  difference  between  the  highest  and  lowest  results 
represents  the  difference  between  the  strongest  and  weakest 
quarries  in  the  country.  No  such  difference  is  to  be  looked  for 
in  the  stones  available  for  any  particular  work  which  come  all 
from  the  same  quarry  or  the  same  formation. 

3.  As  to  Limiting  the  Resultant  to  the  Middle  Third  of  the 
Base.—Let  ABEF,  Fig.  85,  be 
a  vertical  section  of  a  dam,  AB 
indicating  any  horizontal  joint. 
We  may  suppose  the  section 
taken  at  the  highest  part  of  the 
dam,  which  is  supposed  to  rest 
on  firm  rock.  For  convenience 
we  regard  the  section  as  repre- 
senting a  length  of  the  dam  equal 
to  unity,  and  restrict  our  view  to 
he  forces  acting  on  that  length. 
If  the  conditions  of  stability  are 
satisfied  for  this  portion  of  the 

FlGt  85'  dam,  they  will  be  satisfied  for  the 

entire  dam. 

Let  h  =  the  depth  of  water  above  AB; 

/!  =  AB,  the  length  of  the  joint  transversely  to    the 

dam; 

/  =  the  distance  from  A  to  the  centre  of  pressure  on 
the  joint  AB\ 


MASONRY  DAMS.  l8l 

s  —  the  specific  gravity  of  the  masonry ; 
c  =  the  width  of  dam  at  top  EF\ 
W  -—  the  weight  of  masonry  above  AB. 
We  shall  find  it  convenient  to  use  one  cubic  foot  of  water 
as  the  unit  of  pressure.      Thus  if  the  volume  of  masonry  above 
AB  be  represented  by  %h(AB  +  EF),  the  total  weight  will  be 
represented  by  ±h(AB  -j-  EF)s  =  W.      The  moment  of  the 
pressure  of  the  water  with  reference  to  A  is  //  times  $A  times 

/j3 
\h  =  —       We  will  suppose  the  dimensions  to  be  such  that  the 

joint  AB  is  relieved  of  pressure  at  A.  The  total  weight  of  the 
dam  still  rests  on  AB,  but  is  not  uniformly  distributed.  The 
pressure  is  o  at  A,  and  increases  uniformly  toward  B,  where  it 

W 

is  greatest,  the  average  pressure  per  square  foot  being  y.     If 

we  make  Bd'=  2-7-,  the  area  of  the  triangle  ABd'  represents 

*i 

the  total  pressure,  and  the  pressure  at  any  point  in  AB  is 
represented  by  the  vertical  through  that  point  terminated  by 
Ad' .  The  centre  of  pressure  is  the  centre  of  gravity  of 

W 
ABd',  .  •.  /  =  f/r     The  maximum  strain  is  2-j-  and  no  tension 

*i 
exists. 

The  equation  of  moments  with  reference  to  A  is 


/I2 

or       /t2  -f-  r/j  =  — ,      whence     /t  =  —  \c  ± 

Passing  to  figures  and  putting  h  =  100,  c  =  10,  j  =  2.5, 
we  get  ^  =  58.44.  In  the  above  and  following  equations  of 
moments  we  assume  for  simplicity  the  profile  as  a  triangle  so 
far  as  to  regard  the  vertical  through  its  centre  of  gravity  as 

*  The  first  member  of  this  equation  is  the  pressure  of  the  dam  on  its 
base,  or  the  pressure  of  the  base  on  the  dam,  which  is  supposed  to  act  at 
the  extremity  of  the  middle  third. 


1 8  2  AES£X  VOIR-D  A  MS. 

acting  at  £/  from  A.  This  leads  to  but  slight  error,  and  that 
on  the  side  of  safety. 

Total  weight  on  AB  is  -L^/«  =  34-22  X  250  =  8550. 

8550 

Maximum  compressive  strain  =  d  =.  2—^ —  =  293,  being 

.58-44 

a  little  more  than  9  tons  per  square  foot  (short  tons). 

Now  suppose  the  horizontal  pressure  relative  to  the  length 
of  joint  to  be  greater  than  we  have  assumed,  carrying  the 
resultant  pressure  beyond  the  middle  third.  Two  cases  are  to 
be  considered,  i.  Assume  that  the  material  of  the  dam  is  not 
susceptible  of  tensile  strain.  The  base  of  the  triangle  of  pressure 

W 

will   be    3(/t  —  /).      The   average   pressure  will  be   — -. j- 

The  maximum  d  =  —-, y. .      There  will  be  no  strain  on  the 

joint  from  A  to  C,  where  BC  =  3(/t  —  /).  The  strain  at  any 
point  in  BC  will  be  represented  by  a  vertical  through  the  point 
terminated  by  CD.  The  condition  becomes  unsafe  when 
BD  =  d  exceeds  the  safe  compressive  strain  on  the  masonry. 

Still  regarding  the  masonry  as  devoid  of  tensile  strength, 
let  us  find  the  value  of  !l  corresponding  to  a  compressive  strain 
d  on  the  down-stream  end  of  the  joint.  We  have 


1  ( l  +  c'$d* 


whence  /  =  /x  —  (^  4-  c}—.   .     ;     .     .      .     (17) 

And,  since  the  moments  tending  to  turn  the  system  in  one 
direction  about  A  must  be  equal  to  those  tending  to  turn  it  in 
the  opposite  direction, 


Substituting  the  value  of  /  from  (17), 

' 


MASONRY  DAMS.  183 

which  reduces  to  the  form 

(2_^}/i.+  2,(I_*f)/i  =  *  +  «<*?         .      (I8) 

Passing  to  figures,  //  =  100,   c  —  10,   s  =  2.5,   d=  512  =  16 
short  tons  per  square  foot, 

4'  +  6.774  =  2678'      A  —  48-48. 

2.  Regard  the  masonry  as  susceptible  of  tensile  strain,  and 
call  the  maximum  strain  of  compression  d,  of  tension/".  The 
centre  of  pressure  arising  from  the  weight  is  at  the  extremity 
of  the  middle  third ;  the  excess  is  met  by  elastic  strains.  The 
equation  of  moments  with  reference  to  the  centre  O  Fig.  86  is 


whence  (d  +/+  As}!,2  +  cAsl,  =  2//3.  .  .  .  (19) 

Substituting  //  =  100,  s  =  2.5,  c=  10,  d=  282, /=  230  = 
about  100  pounds  per  square  inch,  wre  get  /t  =  49.62.  Show- 
ing that  we  gain  nothing  by  taking  account  of  the  tensile 
strength. 

The  maximum  compressive  strain  is  </  +  /"=  512  =16 
short  tons  per  square  foot.  It  will  appear  from  the  above  that 
the  engineering  canon  which  requires  the  centre  of  pressure  at 
the  base  of  a  dam  to  lie  within  the  middle  third  cannot  be 
regarded  as  an  inflexible  rule,  and  for  dams  not  more  than  IOO 
feet  high  leads  to  excessive  dimensions.  The  reason  alleged 
for  this  rule  is  that  a  pressure  exceeding  this  limit  causes  ten- 
sile strain.  This  is  true  if  the  masonry  is  susceptible  of  tensile 
strain.  It  is  not  true  in  the  sense  that  a  lack  of  tensile  strength 
would,  in  that  condition,  endanger  the  dam.  We  see  that  the 
pressure  can  be  pushed  far  beyond  this  limit  in  a  dam  devoid 
of  tensile  strength  without  passing  the  limits  of  safety. 

In  Fig.  86,  ABEF  represents  the  outline  of  the  dam,  BD 
the  total  compressive  strain  at  B,  and  Af  the  tensile  strain 
at  A.  Of  the  compressive  strain  Bd'  arises  from  the  weight, 


1 84 


A£SE£  VOIR-DA  MS. 


and  Be  —  Af=d'D  from  the  tensile  strain.  /,  where  AI  = 
\AB,  is  the  centre  of  pressure  disregarding  tensile  strain. 
*,  where  Oi  —  %OA,  is  the  centre  of  tensile  strain.  /",  where 
Oi'  =  \OB,  is  the  centre  of  compressive  strain  disregarding  the 
weight. 


FIG.  86. 


FIG.  87. 


We  may  here  advert  to  the  fact  that  in  a  dam  of  triangular 
section  with  one  face  vertical,  the  centre  of  pressure  goes 
through  the  extremity  of  the  middle  third  with  no  water  on  the 
up-stream  side. 

The  computations  are  much  simplified  if  we  suppose  the 
dam  to  terminate  in  a  sharp  crest,  Fig.  87.  Constructive 
reasons  usually  forbid  such  an  arrangement,  but  after  determin- 
ing the  dimensions  on  that  supposition  it  is  easy  to  add  the 
small  triangle  mEF  to  the  profile,  which  has  but  slight  effect 
and  acts  to  increase  the  stability.  The  equation  of  moments  is 


whence     shl*  = 


and 


(20) 


This  is  deduced  on  the  supposition  that  the  centre  of  pressure 
is  at  the  extremity  of  the  middle  third  in  all  horizontal  sections, 
and  eq.  (20)  being  the  equation  of  a  straight  line,  /,  and  //  being 
the  coordinates  of  the  down-stream  face,  we  conclude  that  this 


MASONRY  DAMS.  1  85 

face  is,  subject  to  the  above  condition,  a  straight  line.      The 

maximum  compressive  strain  at  any  depth  h  is  —  .-1  =  sh  =  d. 

*i 

The  compressive  strain,  therefore,  is  proportional  to  Ji.  The 
crushing  pressure  on  the  down-stream  end  of  any  horizontal 
joint  when  the  reservoir  is  full  is  the  same  as  that  on  the 
up-stream  end  of  the  same  joint  when  the  reservoir  is  empty. 
It  is  also  to  be  noted  that  the  centre  of  pressure  on  every  hori- 
zontal joint  is  at  the  down-stream  extremity  of  the  middle  third 
when  the  reservoir  is  full,  at  the  up-stream  extremity  when  the 
reservoir  is  empty.  If  we  adopt  32  OOO  pounds  per  square  foot 
as  the  maximum  crushing  strain,  the  greatest  height  of  a  dam 
with  a  straight  down-stream  face  would  be,  for  s  =  2.5,  h  = 

§12 

—  =  204.8.      Below  this  depth,  in  order  not  to  exceed  the 

crushing  strength  d,  the  down-stream  face  would  require  to  be 
curved.  Above  this  depth,  also,  some  saving  of  material  might 
be  effected  by  drawing  the  down-stream  face  within  the  line 
determined  by  eq.  (20).  Considerations  of  this  character  lead 
to  the  curved  faces  often  adopted  in  high  dams. 

The  following  approximate  method  may  be  used  to  com- 
pute the  outline  of  a  dam  which  will  bring  any  assumed  con- 
stant strain  upon  the  masonry  of  the  down-stream  face.  It  is 
obvious  that  a  strict  adherence  to  this  condition  would  bring 
the  masonry  to  a  sharp  edge  at  the  top,  which  is  inadmissible, 
but  after  computipg  the  outline  upon  this  supposition  any 
desired  small  addendum  can  be  made  to  the  profile  to  obviate 
the  difficulty.  Making  c  —  o  in  eq.  (17),  it  becomes 


='.(•-) 


3^ 

(i3)  becomes  on  the  same  assumption 

k 


(22) 


1 86  A-£SEA  VOIR-DA  MS. 

Equation  (22),  regarded  as  representing  a  line  of  which  // 
and  /  are  the  coordinates,  would  give  an  approximate  outline  of 
a  dam  subject  to  the  assumed  condition,  and  would  not  pass  the 
limit  of  safety  at  any  point.  It  would  materially  overestimate 
the  weight  and  would  not  be  sufficiently  exact. 

It  would  be  fanciful  to  commence  the  curvature  at  the  top 
of  the  dam.  The  face  may  be  assumed  to  run  straight  to  any 
desired  depth,  which  we  will  here  assume  at  50  feet.  At  this 
point,  taking  d  =  512,  s  =  2.50,  we  find,  by  eq.  (22),  /,  = 
23.864.  We  suppose  the  work  to  consist  of  courses  2  feet  in 
depth,  designated  as  course  I,  course  2,  etc.  The  lengths  of 
the  joints  are  designated  /p  /2,  /3,  etc. 

The  weight  of  masonry  above  /x  is  23.864  X  50  X  £  X  2.5 
=  I49M- 

The  moments  tending  to  turn  the  system  to  the  left  about 
A,  Fig.  85,  are: 

/;3 
I.    -2T  =  20833 


2.    1491.5-=    II  864 

Total.  .    32  697 

Moments  tending  to  turn  to  the  right  3/ d.      Here  we 

put  for  /  its  value  as  given  in  (21),  making  the  moment  32  697. 
Adding  a  2 -foot  course,  the  value  of  12  is  approximately 

23.864  -f  2-i-  =  24.818. 

The  mean  length  of  course  i  is  /,  -j-  j  =  24.341. 

Weight  =  2  X  27.371  X  2.5.  =  121.7 
We   now  find  the  moment  as   increased  by  the  addition, 
viz. : 


MASONRY  DAMS.  1 87 

52  X  52  X  52 
Water-pressure  =  -       -^ —  =  23435 

Masonry  above  /x 1 1  864 

Course  No.    I  =   121.7  X  i  X  24.34  =     I  481 

Total 36780 

Total  wt.  of  masonry  above  I2=  1491.5+  121.7  =  1613.2. 

36  780 

Lever-arm    of    moment    =  /=  2—-L —  —  22.80. 

1613.2 

i  1613.2 

—   X    2  =  \  X   6.30  =   2.  10. 


.  •.  True  value  of  /2  =  22.80  +  2. 10  =  24.90. 
/3  approximate  =  24.90  +  12  —  /t  =  25.94. 
Mean  length  of  course  2  =.  25.42. 
Weight  of  course  2  =  25.42  X  2  X  2.5  =  127.10. 
Weight  above  /3  =  1613.2  -(-  127.10  =  1740.30. 
Moments  above  /3: 

1.  Water-pressure  —     =26244 

2.  Above /2  =11864+1481    =13345 

3.  Moment  of  course  2  =  127.10  X  — : —  =     i  615.4 


Total  turning  to  left  ...............  41  204.4 

Lever-arm  of  moment  turning  to  right, 

41  201.4 


I740-3 


And  so  following,  giving  the  ordinates  /  corresponding  to 
the  assumed  abscissas,  h  for  the  curved  outline  of  the  down- 
stream face. 

The  ingenious  reader  will,  no  doubt,  work  out  for  himself 
a  similar  method  founded  on  the  assumptions  of  eq.  (19). 

General  formulas  and  computations  upon  this  subject  neces- 
sarily' rest  upon  a  very  imperfect  basis.  They  assume  a  uniform 


1 8  8  RESER  VOIR-DA  MS. 

height  of  the  dam,  and  take  account  of  a  portion  only  one  foot 
thick  measured  in  the  direction  of  the  dam's  length.  Such  dams 
are  usually  built  to  close  ravines  and  are  of  full  height  only  for 
a  short  distance  in  the  middle,  diminishing  to  nothing  at  the 
ends.  The  formulas  treat  this  portion  of  the  dam  as  though  it 
derived  no  support  from  its  connection  with  the  remainder,  and 
as  though  the  latter  derived  no  support  from  its  connection  with 
the  sloping  sides  of  the  ravine.  The  methods  and  computa- 
tions can  be  fully  developed  only  in  connection  with  some 
particular  case. 

For  facility  of  computation  we  have  taken  s  in  the  preced- 
ing calculations  =  2.5.  This 'would  only  be  justifiable  for  the 
heaviest  stone  and  the  best  work ;  ordinarily  s  would  be  less 
than  here  assumed. 

All  the  above  computations  imply  a  triangular  section, 
vertical  on  the  up-stream  face.  The  approximate  method  just 
presented  gives  the  outline  of  a  dam  in  which  there  is  no  ten- 
sile strain;  no  compression  exceeding  d,  which  is  constant  on 
the  curved  part  of  the  down-stream  face.  Compression  may 
exceed  d  on  the  up-stream  face  when  reservoir  is  empty. 
Resultant  confined  to  middle  third  of  base.  Eq.  (20)  implies 
straight  faces,  no  tension,  compression  not  defined ;  resultant 
confined  to  middle  third  of  base.  Eq.  (22)  assumes  straight 
faces,  no  tension,  compression  not  exceeding  d  when  full; 
resultant  confined  to  middle  third. 


CHAPTER   X. 
EXAMPLES  OF   HIGH   DAMS. 

FlG.  88  and  several  following  figures  are  examples  of  high 
dams  which  have  apparently  been  built  without  much  regard 
to  statical  principles,  but  with  the  sole  purpose  of  getting  in 
material  enough. 


VAL  DE  INFIERNO  DAM. 
FIG.   88. 

Fig.  88  is  a  section  and  Fig.  89  a  plan  of  the  Val  de 
Infierno  Dam,  in  the  province  of  Sorca  in  Spain,  built  for  pur- 
poses of  irrigation.  Figs.  90  and  91  refer  to  the  Gileppe  Dam 
built  at  Verviers  in  Belgium,  for  purposes  of  water-power  and 
water-supply.  It  was  built  of  rubble  masonry  laid  in  mortar. 
Fig.  91  shows  that  the  dam  had  a  curved  outline  in  plan  as  a 
supplement  to  the  strength  of  its  enormous  cross-section. 
Comparing  this  section  with  that  of  the  Otay  rock-fill  dam, 

189 


190 


RESER  VOIR-DAMS. 


Fig.  83,  and  observing  that,  in  the  latter  case,  it  is  only  the 
down-stream  half  of  the  dam  which  resists  the  pressure,  we  see 
that  the  head  of  water  is  sustained,  in  the  latter  case,  by  a  mass 


VALDEINFIERNO  DAM 
FIG.  89. 


GILEPPE  DAM. 
FIG.  90. 

of  loose  stone  no  greater  than  that  of  the  masonry  in  the 
former.  The  dimensions  of  this  dam  were  well  understood  to 
be  unnecessarily  great  by  its  builders,  but  were  demanded  by 
the  interests  which  would  have  been  jeopardized  by  its  failure. 


EXAMPLES   OF  HIGH  DAMS. 


GILEPPE  DAM 
FIG.  91. 


DAM  NEAR  SAN  MATED 

(SAN  FRANCISCO  WATER  WORKS) 

FIG.  92. 


102 


JRESER  VOIR-DA  MS. 


Figs.  92  and  93  refer  to  the  San  Mateo  Dam  near  San  Fran- 
cisco, Cal.,  which  is  also  curved.      Fig.  95  is  a  section  of  the 


FIG.  93.  FlG-  94- 

Hamiz  Dam  in  Algeria,  which  is  not  curved.      This  is  one  of 
the  lightest  sections  of  existing  straight  dams. 


— *-9t&-'-— 4 


HAMIZ  DAM. 
FIG.  95. 

Figs.  96  and  97  *  relate  to  Bear  Valley  Dam,  San  Bernar- 
dino County,  Cal.,  already  referred  to  (see  page  39).  This 
dam  commands  a  drainage-area  of  about  56  square  miles  and 
is  not  intended  to  be  overflowed,  having  a  spillway  separate 
from  the  dam,  as  appears  at  a,  Fig.  97.  It  is  understood  that 
the  water  sometimes  stands  within  a  few  inches  of  the  top,  in 
which  case  the  stone  at  a  depth  of  48  feet  would  be  subjected 

*  Eighteenth  Annual  Report  U.  S.  Geol.  Survey,  Part  IV.  p.  683. 


EXAMPLES  OF  HIGH  DAMS.  X93 

48  I  I 

to  a  pressure  of  335  X  ^  X   1000  X  g-r  X  ^j-^  =  53  tons 
per  square  foot  of  masonry,  making  abstraction  of  the  support 


which  the  masonry  derives  from  the  thicker  course  below. 
The  masonry  is  a  rough  granite  ashlar  with  hearting  of  rubble, 
all  laid  in  cement  mortar. 


FIG.  97. 

Sweetwater  Dam,*  Fig.  98,  on  the  river  of  that  name,  near 
San  Diego,  Cal.,  has  a  profile  somewhat  less  than  would  be 
indicated  by  eq.  (18),  with  s  =  2.25,  being  96  feet  high,  46 
feet  thick  at  bottom,  and  about  10  feet  effective  thickness  at 

*  Eighteenth  Annual  Report  U.  S.  Geol.  Survey,  Part  IV.  p.  688. 


194 


RESER  VOIR-DAMS. 


the  top.     The  dam,  however,  has  a  curved  outline  at  the  top, 
while  eq.  (18)  contemplates  a  straight  outline. 

The  Folsom  Dam  *  on  the  American  River  in  California  is 
noteworthy  for  two  things:  (i)  as  being  the  only  straight  high 
masonry  dam  in  the  Pacific  States;  (2)  as  being  the  only  exist- 
ing application  of  a  movable  shutter  to  a  water-power  dam. 
It  has  a  wasteway  180  feet  wide,  closed  by  a  movable  shutter 


T 


EXTREME  HIGH  WATER 


6  feet  high,    operated  by  hydraulic  jacks.     This   shutter   is 
opened  during  floods,  and  remains  closed  at  other  times. 

Fig.  99 1  is  a  section  of  the  Quaker  Bridge  Dam  now  under 
construction  for  the  water-supply  of  New  York,  believed  to  be 
the  highest  dam  in  the  world.  The  section  is  taken  at  the 
lowest  point  of  the  valley,  where  the  rock  is  overlaid  by  80  to 
87  feet  of  gravel.  Fig.  100  is  an  elevation  of  the  same.  This 
dam  closes  a  ravine  about  1300  feet  wide  at  the  proposed 
water-level.  It  will  form  an  artificial  lake  some  16  miles  long, 
165  feet  extreme  depth,  containing  some  5000  millions  of  cubic 
feet  of  water.  It  commands  a  watershed  of  361  square  miles, 
already  reservoired  to  the  extent  of  some  1800  millions  of 
cubic  feet.  The  greatest  recorded  flood  at  the  dam-site  is  1070 
million  cubic  feet  in  24  hours,  an  average  of  about  600  cubic 
feet  per  second.  The  section  is  the  one  adopted  by  the  board 


*  Eighteenth  Annual  Report  U.  S.  Geol.  Survey,  Part  IV.  p.  687. 
f  Report  of  the  New  York  Aqueduct  Commission,  1889. 


EXAMPLES   OF  HIGH  DAMS. 


195 

the  result  of 


of  aqueduct  commissioners  in    1889,    and  was 
extended  studies  by  engineers  of  reputation. 

Were  the  down-stream  slope  prolonged  to  the  level  of  the 
base,  this  dam  would  have  a  base  width  of  225  feet.  This 
width  is  reached  in  the  view  of  limiting  the  compressive  strain 


SECTION 

FIG.  99. 

to  30000  pounds,  1 3. «4  tons  per  square  foot.  The  curve  or 
batter  of  the  up-stream  face  is  arrived  at  on  the  same  principle. 
The  relation  of  eq.  (20),  putting  s  =  2.5,  would  make  the  width 
corre3pondmg  to  h  =  265  feet,  /j  =  167.6  feet,  and  the  crush- 
ing strain  at  the  base  d  —  662  feet  =18.4  tons  per  square  foot, 
with  no  tensile  strain  on  any  part  of  the  masonry  and  the 
centre  of  pressure  within  the  middle  third  at  every  horizontal 
section. 


196 


XESEX  VO1R-DAMS. 


EXAMPLES   OF  HIGH  DAMS.  1 97 

It  may  be  assumed  that  at  every  such  work  granite  of  i  ooo 
tons  average  strength,  limestone  of  900,  or  sandstone  of  600 
are  always  obtainable.  The  strength  assumed  above  is  less 
than  one-fiftieth  of  the  first,  about  a  fiftieth  of  the  second,  and 
less  than  a  thirty-second  of  the  third. 

Conceding  in  the  most  unqualified  manner  that,  in  a  struc- 
ture of  this  magnitude  and  importance,  stability  should  be 
assured  beyond  the  possibility  of  a  rational  doubt,  the  question 
still  remains :  Can  a  doubt  of  the  ability  of  masonry  to  sustain 
the  fiftieth  or  even  the  thirty-second  part  of  the  ultimate  crush- 
ing strength  of  the  stone  be  regarded  as  a  rational  doubt  ? 

To  what  extent  the  weight  of  the  masonry  below  water 
may  be  regarded  as  diminished  by  buoyancy  is  a  question  which 
has  occasioned  some  perplexity.  In  a  mass  of  uncemented 
stone,  as  the  filling  of  cribwork,  there  is  no  question  but  that 
the  effective  weight  of  the  stone  is  diminished  by  that  of  the 
water  displaced.  In  the  case  of  a  dam  resting  on  the  bottom, 
united  into  a  monolithic  mass  by  mortar  and  joined  to  the 
bottom  by  the  same  means,  the  question  takes  a  different 
aspect.  Mr.  James  B.  Francis,  who  reported  upon  this  work 
some  time  about  1885,  treated  the  submerged  portion  as  of 
diminished  weight.  He  made  experiments  to  demonstrate  his 
view.  In  a  mass  of  concrete  or  mortar  exposed  to  high 
pressure  he  inserted  a  pipe  provided  with  a  pressure-gauge,  and 
found  after  a  time  that  the  gauge  showed  the  full  pressure. 
This  result  was  to  be  foreseen  and  certainly  shows  that  there 
will  be  an  upward  pressure  at  the  base  of  the  dam.  If  a  series 
of  vertical  pipes  were  inserted  in  the  dam  in  a  line  transverse 
to  its  length,  each  pipe  reaching  from  top  to  bottom,  then 
assuming  the  masonry  to  be  perfectly  homogeneous  with  itself 
and  perfectly  united  with  the  bottom,  the  water  would  stand  in 
the.  up-stream  pipe  very  near  the  reservoir  level,  and  in  the 
down-stream  pipe  very  near  low-water  line,  diminishing  with 
an  approach  to  regularity  from  one  to  the  other.  This  shows 
unquestionably  that  there  is  a  pressure  at  the  base  of  the  dam 
tending  to  lift  it ;  but  we  must  reflect  further  that  this  pressure 


198  RESER  VOIR-DA  MS. 

could  not  exist  if  the  mortar  did  not  have  the  tensile  strength 
to  resist  it.  The  perplexity  arises  from  an  attempt  to  reconcile 
two  incongruous  assumptions:  i.  That  the  mortar  is  to  be 
regarded  as  devoid  of  tensile  strength;  2.  That  it  is  to  be 
supposed  capable  of  holding  water  and  sustaining  the  pressure 
thereof.  It  appears  to  me  that  if  we  debit  the  dam  with  the 
upward  pressure  of  water,  we  must  credit  it  with  sufficient 
tenacity  of  mortar  to  resist  the  same. 

If  we  suppose  the  dam  simply  to  rest  on  the  bottom,  with- 
out being  united  with  it  at  all  points,  a  barrier  to  stop  the 
underflow  becomes  necessary  and  the  position  of  this  barrier 
becomes  important.  If  placed  at  the  up-stream  face,  it  ex- 
cludes the  reservoir  pressure  from  the  base  of  the  dam ;  ii  at 
the  down-stream  face,  it  exposes  the  whole  base  to  that  pressure 
and  vastly  increases  the  overturning  forces.  There  can  be  no 
rational  purpose  in  placing  this  barrier  below  the  up-stream 
face,  and  there  can  certainly  be  no  rational  purpose  in  inserting 
a  second  barrier  as  shown  in  the  figure.  If  the  latter  does  not 
serve  its  purpose  of  arresting  water,  it  is  useless.  If  it  does 
serve  that  purpose,  it  is  pernicious  in  exposing  the  dam  to  the 
upward  pressure  of  the  head  in  the  reservoir. 

Discharge  of  a  Wasteway. — Where  water  flows  through  a 
rectangular  notch  in  the  vertical  face  of  a  dam,  which,  for  sim- 
plicity, we  suppose  to  have  no  sensible  thickness,  it  approaches 
the  dam  from  every  direction  that  can  exist  in  a  hemisphere, 
toward  the  centre.  Arriving  near  the  plane  of  the  orifice,  it 
changes  its  direction,  and  "issues  at  right  angles  to  the  latter. 
This  change  of  direction  gives  rise  to  the  phenomenon  of  con- 
traction, making  the  issuing  stream  considerably  smaller  in 
dimensions  than  the  orifice  through  which  it  has  passed.  This 
action  makes  the  flow  of  water  through  an  orifice  very  complex 
and  not  amenable  to  analysis.  The  flow  over  weirs  of  certain 
conventional  form  has  been  made  the  subject  of  experiment,  and 
formulas  which  will  be  referred  to  later  have  been  devised, 
representing  the  discharge  with  a  sufficient  degree  of  accuracy 
for  practical  purposes.  A  wasteway  is  generally  different  from 


DISCHARGE   OF  A    WASTEWAY.  199 

the  ideal  weir,  and  the  weir  formula  requires  some  modification 
in  its  application  to  this  case.  Where  the  entrance  to  the 
wasteway  is  rounded  or  expanded  toward  the  reservoir,  the 
effect  of  contraction  may  be  disregarded,  and  in  that  case  we 
can  compute  the  flow  with  considerable  accuracy.  We  will 
consider  first  the  flow  over  an  ordinary  dam,  the  width  of  the 
top,  which  must  be  regarded  as  the  length  of  the  channel  of 
discharge,  being  so  small  that  the  frictional  head  or  resistance 
to  movement  may  be  disregarded. 

Let  //  =  the  height  of  water  in  the  reservoir  above  the  sole 

of  the  wasteway ; 
v  =  the  velocity  with  which  the  water  issues  from  the 

wasteway ; 

x  —  the  depth  corresponding  to  the  velocity  v\ 
Q  =  the  discharge ; 

w  =.  the  width  of  the  channel  of  discharge. 
Then  we  must  have 


and     Q  =  wx  V2g(k  —  x}.        (23) 

h  —  x  in  this  expression  determines  the  velocity  of  the  stream. 
x  determines  the  cross-section.  On  what  principle  will  the 
stream  resolve  itself  into  these  two  elements  ?  The  division 
will  be  governed  by  a  principle  of  universal  application  in 
nature,  viz.,  the  result  of  any  given  expenditure  of  energy  is 
the  greatest  that  is  possible  consistent  with  the  existing  condi- 
tions. In  other  words,  Q  must  be  a  maximum  with  reference 

to  x,  a  condition  expressed  by  -3—  =  o.      From  (23), 


=«, 


whence  h  —  x  =  —     and     x  —  \h (24) 


v  —  \  /  2g—  —  Vgx 


Therefore     v  —  \  /  2g—  —  Vgx     and     Q  =  wxv  =  wx  Vgx; 


20O  KESEK  VOIR-DA  MS. 


,-v^ 


and  since     v  =  'x/  2g— 


/ 


-  -3-087 w$.  .    .    .    (25) 

Eq.  (24)  shows  that  one-third  of  the  head  is  expended  in 
velocity;  the  remaining  two-thirds  determines  the  cross-sec- 
tion. Eq.  (25)  is  only  true  for  the  case  in  which  the  width  of 
the  dam  or  length  of  the  channel  of  discharge  is  too  small  to 
have  any  influence  upon  the  discharge. 

Formula  (25)  may  be  tested  by  comparison  with  results  of 
experiments  made  by  James  B.  Francis  in  1852  on  the  flow  of 
water  over  a  weir  intended  to  represent  a  dam.  The  width, 
which  we  represent  by  ti',  was  about  10  feet  (9.995).  The 
width  of  the  level  crest,  which  we  represent  by  /,  was  only 
3  feet,  joined  on  the  up-stream  side  by  a  slope  of  some  3  to  I. 
The  flow  was  actually  measured  in  a  reservoir,  viz.,  a  disused 
lock-chamber. 

, Cubic  Feet  per  Second. , 

For  h  =  0.5872,  Q  by  measurement  =  13.385,  by  eq.  (24)  =  13.883 
0.7903,       "  "  20.892,   "         "  21.672 

0-9767,       "  28.914,   "  29.782 

1.3252,       "  "  46-183.   "         "  47.069 

1.6338,       "  64.346,   "         "  64.434 

Questions  often  arise  as  to  the  time  required  for  the  water 
in  a  reservoir  to  rise  or  fall  with  a  given  width  of  wasteway 
and  given  influx  of  water.  A  method  of  solving  such  ques- 
tions by  rough  approximation  has  been  already  indicated  (see 
page  159).  We  will  now  attempt  to  deduce  a  more  exact 
formula  for  such  cases. 

Let  A  —  area  of  reservoir  surface  in  square  feet,  not  con- 
sidering the  change  in  A  incident  to  any  slight 
rise  or  fall  of  the  surface ; 
w  =  width  of  wasteway  in  feet  supposed  to  admit  of 

the  application  of  formula  (24)  ; 

Q  =  constant  influx  of  water  in  cubic  feet  per  second ; 
h  =  depth  on  wasteway  in  feet; 


DISCHARGE    OF  A    WASTEWAY.  2OI 

t  =  time  in  seconds  corresponding  to  /z,  reckoned  from 
the  moment  the  water  commences  to  flow  over 
the  wasteway; 
/^  =  depth  corresponding  to  the  quantity  Q. 

We  have  the  relation  (Q  —  3.087^^)^  =  Adk. 

dt_  __  dh 

'  A  ~  Q  _  3.087^' 

Put  h  =  x>,      3.0870;  =  0,  =  b\      Then 


a  xdx  xdx 

dt  =     =    =     -       *  ~ 


x  I  mx  +  h 

Assume  -^  --  ,  =  7  ---  —  o~~i  —  7  —  ;  —  j-9>     whence 
tf-  —  x*       b  —  x   '   x*  -|*  ^  -j-  bz 

x  =  l(x*  -\-bx-\-  b^  +  mx(b  -  x]  -f  h(b  —  x]. 

Putting  coefficients  of  the  like  powers  of  x  separately  equal 
to  o,  we  find 

/  =  —7,      m  =  I  =  —r,     11  =  --  ,      and  (26)  becomes 

^_///_         dx         -1-         (-y  —  b}dx 

2  A       ~  "* 


dx 


^A  bx      &  +  bx  +  &' 

^ab  dx  i  (2.x  —  2b]dx 

~jT  (tt    ^^    "^  "T"  9        j         ^  ;         TA 

2^4  ^  —   X    '    2  ;tr2  -f-  bx  +  ^2 

^          i    (2x  +  3)^         i 

~T 


~  *  —  x    '    2  ^r2  +  bx  +  £2        2  ^2  +  bx  -f  ^2' 
By  integration, 


2/4 


202  RESER I  'OIR-DAMS. 


=  log 


To  determine  C,  the  constant  of  integration,  we  must 
remember  that  x  —  V7i,  b  —  \'Tiv  and,  since  h  —  o  when 
/  =  o,  eq.  (27)  becomes  in  that  case 

~1 


.  •.  C  =  173  tan"1  — -=  =  473  arc  30° 
and  we  have 


-,'Jtan-^.     (28) 
Putting  //  =  7/j,  (28)  becomes 

^  =  ,og  3^'  +  vTtan-  ^L  _  4/3- tan-.  </J. 

The  first  term  of  the  second  member  is  infinite  and  the  two 
second  terms  reduce  to 


4/3   tan-1  -=  -  tan'1  l7^    =  I73(3O°  -  60°)  =  —  0.88625. 

This  shows  that,   in    mathematical    strictness,   the  efflux    can 
never  become  equal  to  the  influx,  though  //  can  become  equal 


DISCHARGE   OF  A    WASTEWAY.  2O3 

to  any  assignable    fraction  of  h^.      Let   h  be  assumed  =  chv 
where  c  is  less  than  unity ;  then  (28)  becomes 


,        \  en.  -4-  r  H    v  tit.  -f-  n,  . 

=  log  -       = — ^= —  —  —  0.88625    (approximate) 


=   log  _  Q.88625 (29) 

I    —    \*C 

Assume,  as  at  page  158,^  =  200  acres  =  8712  ooo  square 
feet,  influx  =  10  ooo  cubic  feet  per  second,  7^  =  4.5,  h  = 
4.375,  whence  .c  —  0.9722,  Vc  —  0.9860. 

A  discharge  of  10  ooo  cubic  feet  per  second  under  a  head  of 

10  ooo 
4.5  feet  implies  a  wasteway  —  — -=.  =  339.35  feet  m 

3.087  X  4-5  ^4-5 
width.      .  •.  w  =  339.35. 


nat  log  <•*"  +  -S**>±L    =  nat  ,o 


I     — 

^sftair1  ^3  —  tan'1  —-=?}  =  0.88625 
V  1/37      _ 

3.92401 

2  x  8  712  ooo 
t  =  3.92401  X   •  -  -  -  =   10256    seconds. 

3  X  339-35  X  3-087^4.5 

We  found  by  the  rough  method  employed  (page  I  59)  that 
10  06  1  seconds  would  be  required  to  raise  the  water  to  a  height 
of  4.25  on  the  weir.  The  last  result  is,  no  doubt,  more 
correct. 


CHAPTER   XL 
FAILURES  OF   HIGH   DAMS. 

THE  successful  execution  of  a  high  dam  is  not  necessarily 
an  instructive  example  to  engineers,  especially  if  success  be 
attained  by  excessive  and  inordinate  use  of  material  and  by 
expense  far  beyond  any  rational  requirement.  In  that  case  the 
example  is  misleading,  as  inspiring  the  belief  that  such  dimen- 
sions and  outlays  are  unavoidable,  although  it  must  be  freely 
conceded  that  a  great  excess  in  such  a  work  is  better  than  a 
small  deficiency.  The  failure  of  a  dam,  however,  when  its 
causes  are  clearly  understood,  cannot  be  otherwise  than  in- 
structive to  the  engineering  profession  and  to  the  community 
at  large,  however  disastrous  to  those  immediately  concerned. 
We  will  therefore,  assuming  the  reader's  approbation,  devote 
this  chapter  to  an  account  of  some  of  the  more  conspicuous  and 
instructive  instances  of  the  failures  of  high  dams,  commencing 
with  earth  embankments. 

The  Efflux  has  usually  proved  to  be  the  weak  point  of  earth 
embankments,  and  it  is  here  that  breaks  have  usually  started. 
Imperfect  consolidation  of  the  bank  and  the  absence  of  any 
effective  special  skin  or  diaphragm  to  stop  the  water  some- 
times allows  the  whole  mass  to  become  "waterlogged,"  every 
part  of  the  work  becoming  saturated  and  under  pressure.  The 
water  appears  on  the  outside  and  gathers  into  rivulets.  The 
whole  becomes  semifluid.  Masses  slough  off  the  outside  and 
the  dam  flows  away.  Defective  wasteways  allowing  the  water 
to  rise  till  it  overtops  the  embankment  are  also  a  common 
cause  of  failure. 

204 


THE  BRADFIELD   RESERVOIR.  2O5 

Very  instructive  was  the  failure  of  the  Berthaud  Reservoir,* 
one  of  the  most  important  of  those  pertaining  to  the  central 
canal  of  France.  This  resulted  neither  from  defective  efflux, 
improper  construction,  nor  insufficient  wasteway.  On  the  I4th 
of  April,  1829,  a  flood  occurred  which  taxed  the  wasteway  to 
near  its  full  capacity,  and  while  the  water  was  at  its  highest, 
and  but  little  below  the  top  of  the  embankment,  a  violent  wind 
carried  the  waves  over  the  latter.  The  reflex  action  of  the 
waves  destroyed  the  pavement  on  the  interior  face,  and  the 
water  which  went  over  wore  down  the  earthwork  till  a  breach 
was  made. 

A  small  reservoir  in  Massachusetts  failed,  some  twenty-five 
or  thirty  years  ago,  from  a  cause  that  might  operate  in  any  such 
work,  and  should  not  be  forgotten.  A  tract  of  woodland  was 
flowed  and  the  trees  were  killed.  In  the  course  of  time  a 
large  quantity  of  driftwood  accumulated  from  the  trees  that  fell 
into  the  water.  During  a  period  of  high  water  and  high  wind 
this  was  carried  into  the  wasteway  in  such  masses  as  to  choke 
the  latter  and  raise  the  water  over  the  embankment. 

The  Bradfield  Reservoir,!  near  Sheffield,  England,  built  for 
the  water-supply  of  that  city,  and  also  for  water-power,  had 
an  embankment  about  90  feet  in  height,  13  feet  wide,  and  1250 
feet  long  on  top,  with  slopes  of  2\  to  I.  A  puddle-wall,  about 
4  feet  thick  at  top,  18  feet  at  the  lowest  ground-level,  extended 
from  top  to  bottom,  from  end  to  end,  and  60  feet  into  the 
ground.  The  remainder  of  the  embankment  was  earth  dumped 
from  carts  without  any  attempt  at  consolidation.  The  efflux 
was  by  means  of  cast-iron  pipes  at  the  base  of  the  embank- 
ment, about  500  feet  in  length,  surrounded  by  clay  puddle. 
The  reservoir  was  being  filled  for  the  first  time,  and  on  the  I2th 
of  March,  1864,  the  water  had  risen  to  within  5  or  6  feet  of  full 
height,  the  contents  amounting,  at  that  time,  to  something 
over  100  million  cubic  feet.  A  slight  vortex  suddenly  appeared 
in  the  surface  of  the  water,  indicating  a  leak.  Workmen  were 

*  See  Genie  Civil,  vol.  xxvn.  f  Ibid. 


206  FAILURES  OF  HIGH  DAMS. 

immediately  summoned  to  arrest  it,  and  a  messenger  was  sent 
tofwarn  the  inhabitants.  So  rapid  was  the  enlargement  of  the 
opening  that  the  workmen  barely  escaped  with  their  lives  and 
the  escaping  waters  outstripped  the  messenger.  In  30  minutes 
the  entire  volume  of  the  reservoir  had  escaped.  On  one  great 
farm  lying  in  the  track  of  the  flood,  out  of  103  persons  only 
3  escaped.  The  flood  reached  Sheffield  at  midnight,  without 
warning,  and  inundated  all  the  streets.  Some  70  ooo  cubic 
yards  of  the  embankment  was  carried  away  and  deposits  7  or 
8  feet  deep  were  made  in  the  streets  of  the  city.  The  number 
of  houses  destroyed  in  whole  or  in  part  was  798,  and  238  per- 
sons lost  their  lives. 

Messrs.  Rawlinson  and  Beardmore,  two  engineers  who  took 
part  in  the  official  inquiry  into  this  disaster,  attributed  it  to  the 
disposition  of  the  efflux-pipes,  or  perhaps  more  properly  speak- 
ing to  the  fact  that  pipes  through  the  embankment  were  used 
for  the  efflux,  which  they  say  should  not  have  been  done  in  a 
work  of  this  magnitude.  The  writer  is  also  of  opinion  that  in 
so  important  a  reservoir  the  efflux-pipes  should  be  laid  in  a 
tunnel  or  deep  cut  in  the  natural  ground.  The  difference  in. 
strength  between  an  embankment  with  a  puddle-wall  and  one 
with  a  facing  of  puddle  should  be  attentively  considered.  In 
the  former  case  the  down-stream  half  of  the  embankment  sus- 
tains the  entire  pressure  of  the  water  in  addition  to  the  pressure 
of  the  up-stream  half.  In  the  latter  case  the  entire  strength  of 
the  embankment  is  opposed  to  the  pressure  of  the  water.  In 
addition  to  this  the  pressure  in  the  former  case  acts  horizontally  ; 
in  the  latter,  at  right  angles  to  the  slope.  In  an  unconsolidated 
embankment  like  the  above  a  well-jointed  diaphragm  of  heavy 
timber  would  be  preferable  to  a  puddle-wall. 

An  earth-bank  failure  occasioning  much  perplexity  to 
engineers  occurred  at  Portland,  Me.*  This  was  the  service- 
reservoir  of  the  Portland  Water  Company,  a  comparatively 
unimportant  work,  partly  in  excavation  and  partly  in  embank- 

*  Engineering  News,  N.  Y.,  vol.  xxx,  1893. 


THE  BRADFIELD   RESERVOIR.  2O/ 

ment,  the  extreme  height  of  the  latter  being  some  45  feet. 
The  reservoir  held  some  40  feet  depth  of  water,  about  20  million 
gallons.  The  embankment  was  built  with  slopes  of  \\  to  i. 
The  inner  slopes  were  faced  with  puddle  of  the  extraordinary 
thickness  of  6  feet  surmounted  by  a  thin  layer  of  broken  stone, 
and  the  latter  by  a  substantial  block  pavement.  The  embank- 
ment rose  5  feet  above  the  water-level,  and  there  had  a  thick- 
ness of  10  feet  including  the  puddle,  which,  above  the  water- 
level,  occupied  the  whole  thickness  of  the  bank.  The  work 
rested  upon  a  very  refractory  clay  gravel,  and  the  embankments 
had  been  formed  of  material  obtained  from  the  excavation, 
deposited  in  thin  layers  and  very  thoroughly  rolled.  At  one 
angle  of  the  reservoir  was  the  drain-pipe,  8  inches  diameter, 
at  the  level  of  the  bottom,  and  imbedded  some  18  feet  in  the 
natural  ground.  Also  the  overflow-pipe  leading  from  the 
water-level  on  the  inside  to  the  drain-pipe  level  on  the  outside. 
Both  these  pipes  lay  in  the  diagonal  line  of  the  junction  of  the 
two  embankments.  The  reservoir  was  built  in  1889  and  had 
been  in  use  till  the  time  of  the  accident.  On  the  6th  of 
August,  1893,  at  5. 30  in  the  morning,  some  persons,  happening 
to  be  early  astir,  noticed  a  considerable  stream  of  water  issuing 
from  the  ground  at  the  above-mentioned  angle.  Instant  alarm 
was  given  to  the  endangered  houses,  but  before  all  the  people 
could  be  made  to  understand  their  danger  the  whole  volume 
of  the  water  was  in  motion  and  several  persons  were 
drowned. 

The  only  rational  theory  of  this  break  that  could  be  framed 
was  that  the  pressure  of  the  water  on  the  two  embankments 
tended  to  separate  them  on  the  exact  diagonal  line  of  the  two 
pipes;  that  consequently  the  earth  in  this  plane  had  less 
coherence  and  offered  less  resistance  to  the  passage  of  water 
than  elsewhere.  This  fact,  combined  with  the  natural  tendency 
of  the  water  to  follow  the  pipes,  probably  occasioned  the  dis- 
aster. The  superiority  of  natural  methods  of  consolidating 
earth  over  artificial  methods  was  clearly  seen  here  in  the  fact 
that,  though  the  current  was  able  to  cut  a  gap  30  feet  wide 


2O8  FAILURES   OF  HIGH  DAMS. 

through  the  embankment  in  a  few  minutes,  it  made  but  slight 
impression  on  the  natural  gravel. 

A  conspicuous  instance  of  failure  resulting  clearly  from 
improper  construction  was  that  of  the  Mill  River  Dam,*  at 
Williamsburg,  Hampshire  County,  Mass.,  on  a  branch  of  Mill 
River,  a  small  stream  entering  the  Connecticut  at  Northampton. 
It  was  built  in  1865  by  the  Williamsburg  Reservoir  Company, 
a  corporation  chartered  for  the  purpose,  the  stock  in  which  was 
held  by  manufacturers  whose  mills  are  located  on  the  stream 
below,  the  reservoir  being  built  for  the  purpose  of  giving  them 
a  larger  supply  of  water  during  the  dry  season. 

The  dam  was  43  feet  extreme  height,  500  or  600  feet 
long  on  top,  with  a  wasteway  33  feet  wide  in  natural  ground. 
It  was  an  earth  embankment  with  slopes  of  i^  on  I.  It  had  a 
wall  of  rubble  masonry  through  the  centre  longitudinally,  2 
feet  thick  at  top  and  widening  downward,  at  the  rate  of  i  inch 
per  foot.  The  discharge  was  through  an  iron  pipe  laid  in  the 
lowest  part  of  the  ravine.  The  site-  of  the  work  was  a  glacial 
gravel  of  very  firm  texture  overlaid  by  a  few  feet  of  porous 
gravel.  No  engineer  or  person  so  designated  was  employed 
on  the  work.  A  committee  of  the  manufacturers  entered  into 
a  contract  for  its  execution,  and  an  occasional  visit  of  some  one 
of  the  members  was  the  only  inspection  maintained.  Gross 
defects  of  workmanship  were  disclosed  by  the  accident.  The 
Avail  was  not  laid  in  mortar,  but  built  up  dry  and  grouted.  The 
cavities  were  not  filled  and  the  mortar  was  not  good.  The 
loose  gravel  was  not  removed  from  the  central  part  of  the  site, 
and  the  wall  did  not  extend  to  the  impermeable  gravel.  No 
proper  means  were  used  for  consolidating  the  embankment. 

On  the  i6th  of  May,  1874,  between  7  and  8  A.M.,  the 
water  being  4  feet  below  the  top  of  the  dam,  masses  of  earth 
were  observed  to  slide  from  the  outer  slope  of  the  embankment. 
A  milkman,  on  his  morning  round,  stripped  the  harness  from 
his  horse,  mounted,  and  started  at  full  speed  down  the  valley, 

*  Report  of  Committee  in  Trans.  Am.  Soc.  C.  E.,  1874. 


THE   SOUTH  FORK  DAM.  2OO, 

giving  warning  to  the  inhabitants  and  the  mill  people,  which 
doubtless  saved  many  lives.  In  20  minutes  three-fourths  of 
the  reservoir  contents,  then  amounting  to  about  100  million 
cubic  feet,  were  discharged,  drowning  143  persons  and  destroy- 
ing property  to  the  amount  of  about  a  million  dollars. 

This  was  a  very  conspicuous  instance  of  failure  from  im- 
proper construction,  and  the  only  wonder  is  that  the  dam  stood 
so  long.  The  immediate  cause  of  the  disaster  was  the  attain- 
ment of  that  state  of  complete  saturation  which  reduced  the 
earth  to  a  semifluid  condition  as  shown  by  the  sloughing  off  of 
masses  of  earth.  Why  this  condition  was  deferred  so  long  is 
not  easy  to  say.  The  water  had  many  times  stood  'higher  than 
on  the  day  of  the  disaster.  Ordinarily  a  bank  destined  to  fail 
from  this  cause  fails  on  the  first  trial.  If  it  survives  that  trial, 
causes  are  constantly  in  operation  which  make  it  safer,  viz., 
natural  settlement  and  tightening  by  sediment  borne  in  the 
water.  The  impounded  stream,  however,  was  of  remarkable 
clearness,  bearing  no  appreciable  sediment. 

The  South  Fork  Dam.* — The  crowning  reservoir  disaster  of 
the  nineteenth  century  was  the  failure  of  the  South  Fork  Dam, 
in  Cambria  County,  Pennsylvania,  on  the  headwaters  of  the 
Conemaugh,  a  tributary  of  the  Allegheny.  This  reservoir 
covered,  at  ordinary  high-water  level,  about  407  acres;  at 
5  feet  above,  457.  It  had  a  drainage-area  of  48.6  square 
miles,  extending  to  the  summit  of  the  Alleghenies,  the  surface 
of  the  full  reservoir  being  about  1600  feet  above  the  tide-level. 
On  the  same  stream  some  3  miles  distant  is  the  important  city 
of  Johnstown,  containing  at  the  date  of  the  accident  something 
over  20  ooo  people.  The  natural  declivity  of  the  stream  from 
the  outlet  of  the  reservoir  to  Johnstown  is  something  over  400 
feet.  This  reservoir  was  built  by  the  State  of  Pennsylvania  as 
a  feeder  to  its  canal  system,  being  completed  in  1852  or  early 
in  1853,  and  it  was  used  for  that  purpose  till  1857.  It  was 
formed  by  an  embankment  across  a  narrow  ravine,  with  a 

*  See  Paper  477,  vol.  xxiv,  Trans.  Am.  Soc.  C.  E. 


210  FAILURES  OF  HIGH  DAMS. 

waste  way  in  the  natural  rock,  around  the  end  of  the  dam. 
The  dam  was  about  70  feet  in  extreme  height;  the  inner  half 
was  of  earth  with  a  slope  of  2  to  I ,  the  outer  of  loose  heavy 
stone  with  a  slope  of  if.  The  discharge  was  through  a  brick 
culvert  founded  upon  the  rock,  reaching  to  within  65  feet  of  a 
gate-chamber  at  the  toe  of  the  embankment,  and  communicat- 
ing with  the  same  by  five  24-inch  cast-iron  pipes.  From  the 
gate-chamber  arose  a  tower  communicating  with  the  embank- 
ment by  a  bridge  and  containing  the  mechanism  for  operating 
the  sluices.  The  inner  slope  and  crown  were  covered  with  a 
pavement  15  or  1 8  inches  thick  resting  on  a  layer  of  stone 
fragments.  •  The  earthwork  was  of  suitable  material  very 
thoroughly  compacted,  and  the  whole  work  was  faithfully 
executed. 

In  1857  the  reservoir,  together  with  the  canal  to  which  it 
pertained,  was  transferred  to  the  Pennsylvania  Railroad  Com- 
pany, and  continued  to  be  used  by  that  company.  Shortly 
after  the  transfer,  leaks  occurred  where  the  cast-iron  pipes 
entered  the  culvert,  and  in  July,  1862,  there  was  a  serious 
break  at  this  point  which  washed  out  the  upper  end  of  the 
culvert  and  part  of  the  embankment.  The  reservoir  being  only 
partly  filled  at  this  time,  the  contents  were  discharged  through 
this  breach  with  no  serious  damage.  The  abandonment  of  the 
canal  being  then  under  contemplation,  the  company  did  not 
repair  the  embankment,  and  it  remained  for  a  long  time  in  this 
condition.  The  reservoir  went  out  of  the  company's  possession 
in  1875,  and  in  1880  the  property,  consisting  of  500  acres  of 
land  covering  the  reservoir-site,  came  into  possession  of  an 
organization  called  the  South  Fork  Hunting  and  Fishing  Club 
of  Pittsburgh,  Pa.  This  club  discontinued  the  outlet-sluices, 
removed  the  pipes,  gates,  and  tower,  and  maintained  the  reser- 
voir at  a  uniform  level,  discharging  the  surplus  water  through 
the  wasteway. 

The  original  specifications  of  the  dam  provided  for  two 
wasteways  of  the  aggregate  width  of  1 50  feet,  or  for  a  single 
wasteway  of  equal  width.  This  provision  was  not  carried  out. 


THE   SOUTH  FORK  DAM.  211 

The  wasteway  existing  at  the  date  of  the  disaster  was  about 
120  feet  wide  at  the  upper  end,  176  feet  long,  and  69  feet  wide 
at  the  lower  end,  being  a  channel  cut  in  the  rock  with  the 
bottom  level.  The  specifications  also  required  the  crest  of  the 
dam  to  be  10  feet  wide  and  10  feet  above  the  bottom  of  the 
wasteway.  The  width  was  adhered  to,  but  in  adapting  the 
dam  to  a  roadway  the  height  was  reduced  to  not  over  8  feet 
above  the  wasteway.  The  latter  was,  moreover,  obstructed 
by  the  supports  of  a  bridge  appertinent  to  the  roadway  and  by 
screens  to  prevent  the  escape  of  fish.  In  other  words,  the 
wasteway  was  only  half  that  originally  contemplated  and  had 
been  encroached  on  in  three  ways :  by  closing  the  sluices,  by 
lowering  the  embankment,  and  by  the  said  obstructions.  The 
owners  established  a  clubhouse  at  the  dam  with  keeper  and 
attendants,  and  used  the  property  as  a  place  of  recreation. 
Such  was  the  condition  on  the  3Oth  day  of  May,  1889. 

On  the  3Oth  and  3ist  of  May  and  the  ist  of  June  a  rainfall 
of  extraordinary  severity-oec-utred  in  this  part  of  Pennsylvania, 
extending  into  Virginia,  West  Virginia,  and  Maryland,  over 
an  area  of  some  20  ooo  square  miles.  The  Potomac  rose  to 
an  unprecedented  height,  being  16  feet  deep  on  the  U.  S. 
dam  at  the  head  of  Great  Falls  on  June  2d.  The  very 
able  committee  of  the  American  Society  of  Civil  Engineers  * 
who  investigated  this  disaster  collected  all  available  records 
of  rainfall  upon  the  entire  storm-area,  embracing  about  fifty 
stations.  No  station  existed  on  the  South  Fork  drainage-area, 
but  the  record  of  contiguous  stations  indicated  6  or  8  inches  on 
that  area.  It  appeared  that  the  rain  must  have  fallen  at  times 
during  the  night  of  May  30-3 1  at  the  rate  of  £  inch  an  hour. 
The  declivities  of  the  drainage-area  were  very  steep  and  shed 
water  into  the  streams  with  great  rapidity.  On  the  morning 
of  the  3  ist  the  influent  stream  was  a  roaring  torrent  and  the 
water  was  rapidly  rising  on  the  wasteway.  Workmen  were 
collected  and  efforts  made  to  open  a  passage  for  the  water 

*  Trans.  Am.  Soc.  C.  E.,  vol.  xxiv.  p.  421. 


212  FAILURES   OF  HIGH  DAMS. 

around  the  opposite  end  of  the  dam  from  the  existing  wasteway, 
and  a  channel  was  formed  which  the  water  rapidly  widened  and 
soon  discharged  a  large  volume.  A  slight  breast,  was  also 
raised  on  the  dam  by  plough  and  shovel  which  retarded  the 
disaster.  By  1 1.30  A.M.  the  water  was  flowing  over  the  entire 
length  of  the  dam,  and  at  3  P.M.  a  breach  occurred  which 
emptied  the  reservoir  in  the  course  of  45  minutes. 

The  city  of  Johnstown  was  already  inundated  to  a  large 
extent  by  the  unprecedented  flood,  some  of  the  streets  being 
10  feet  under  water  when  the  break  occurred,  which  made  it 
impossible  for  the  inhabitants  to  escape  with  readiness  even  had 
timely  warning  been  given.  When  the  reservoir  flood  arrived, 
bringing  houses,  bridges,  trestles,  and  other  wreckage  with 
many  people  clinging  to  it,  an  enormous  mass  of  debris  lodged 
against  a  massive  arched  railroad  bridge  which  spanned  the 
stream  and  still  further  raised  the  water.  This  great  raft, 
constantly  augmented  by  the  arrival  of  entire  houses  with  their 
inmates,  took  fire  and  burned  amid  scenes  of  terror  and 
desperation  which  those  who  witnessed  did  not  readily  forget. 

That  this  disaster  was  due  to  an  insufficient  wasteway  is 
entirely  clear.  The  committee  estimate  the  maximum  influx, 
which  did  not  occur  till  after  the  disaster,  at  10000  cubic  feet 
per  second.  The  wasteway  could  not  have  discharged  a 
quantity  exceeding  what  would  be  indicated  by  formula  (25), 
with  w  =  70  and  h  —  8,  viz.,  3.087  X  70  X  8  V8  =  4889 
cubic  feet  per  second.  The  execution  and  maintenance  of  the 
work  according  to  the  original  specification,  viz.,  I  50  feet  width 
of  wasteway  10  feet  below  the  crest  of  the  dam,  would  in  con- 
cert with  the  sluices  undoubtedly  have  saved  the  work. 

A  failure  from  an  insufficient  wasteway  is  more  disastrous 
than  from  any  other  cause,  the  quantity  of  water  liberated  in 
that  case  being  the  utmost  capacity  of  the  reservoir. 

Although  this  disaster  chiefly  emphasizes  the  necessity  for 
an  ample  wasteway,  the  case  is  no  exception  to  the  general 
statement  that  the  sluices  are  the  critical  point  of  an  earth 
embankment,  the  dam  having  once  before  failed  at  that  point. 


THE  PUENTES  DAM  IN  SPAIN.  2 13 

The  most  reliable  estimate  places  the  number  of  lives  lost 
in  this  disaster  at  214.2,  and  the  property  loss  at  between  three 
and  four  millions  of  dollars. 

High  masonry  dams  are  not  exposed  to  so  many  causes  of 
failure  as  earth  embankments,  and  failures  of  the  former  are 
much  more  rare  than  those  of  the  latter  class.  Such  failures 
may  always  be  ascribed  to  one  of  three  causes:  (i)  inadequate 
dimensions;  (2)  defective  foundations;  (3)  improper  materials 
or  workmanship. 

The  Puentes  Dam  in  Spain.* — Fig.  101  is  an  example  of  a 
failure  from  defective  foundations.  This  dam  was  built,  toward 


PUENTES  DAM 
FIG    101.  • 

the  close  of  the  last  century,  for  purposes  of  irrigation.  It 
closed  a  valley  on  a  branch  of  the  Segura  River  in  the  province 
of  Murcia,  which  contained  in  the  lower  part  of  its  cross-section 
a  deposit  of  earth,  while  rock  appeared  at  a  higher  level. 
Instead  of  excavating  to  the  bed-rock  throughout,  it  was 

*  Genie  Civil,  vol.  xxvn. 


214  FAILURES   OF  HIGH  DAMS. 

decided  to  rest  the  central  part  of  the  dam  on  piles,  while  the 
flanks  rested  on  rock.  The  piles  penetrated  about  22  feet,  but 
in  the  centre  did  not  reach  the  rock.  The  section  of  the  dam, 
as  will  appear  from  the  cut,  was  abundantly,  in  fact  unneces- 
sarily, heavy.  In  the  centre  of  the  dam  was  a  well  for  operat- 
ing the  sluice-gates.  It  was  intended  to  hold  the  water  to  a 
height  of  about  160  feet,  but  the  dam  had  stood  for  eleven 
years  without  being  filled  to  a  height  of  more  than  100  feet, 
and  during  this  time  sediment  had  accumulated  to  a  depth  of 
over  40  feet  at  the  outlet.  In  April,  1802,  heavy  rains  nearly 
filled  the  reservoir.  About  half- past  two  P.M.  of  April  3Oth 
volumes  of  water  were  observed  to  issue  near  the  wooden  plat- 
form which  received  the  discharge.  The  custodian  of  the  dam 
was  sent  for,  and  a  messenger  was  despatched  to  warn  the 
inhabitants  of  Lorca,  a  village  of  importance  on  the  stream. 
About  3  o'clock  a  violent  explosion  was  heard  in  the  gate- 
well,  and  the  water  suddenly  increased  in  volume.  Soon  a 
second  explosion  shook  the  earth,  and  an  enormous  mass  of 
water  burst  forth,  bearing  piles  and  timber  of  the  foundation. 
A  third  explosion  and  a  mountain  of  water  appeared,  "  of  a 
color  red  like  fire  frightful  to  behold,"  says  the  record.  The 
reservoir  was  empty  in  an  hour,  and  the  dam  remained  in  the 
form  of  an  arch  of  some  200  feet  span,  suspended  over  the 
chasm.  The  water  reached  Lorca  in  advance  of  the  messen- 
ger, who  was  driven  to  the  hills,  and  some  six  hundred  per- 
sons were  drowned. 

Fig.  102  is  a  section  of  the  Habra  Dam*  in  Algiers,  com- 
pleted in  1871.  In  1872  several  feet  in  depth  of  the  weir 
yielded  to  the  pressure  of  the  water,  allowing  a  great  quantity 
to  escape,  some  200  ooo  cubic  feet  per  second,  which  did  little 
damage.  December  16,  1881,  a  flood  went  8  feet  deep  over 
the  weir,  and  the  unexpected  pressure  caused  a  portion  360 
feet  long,  50  feet  deep,  to  separate  from  the  structure,  liberat- 
ing a  volume  of  water  which  drowned  some  four  hundred 


Genie  Civil,  vol.  xxvn.  p.  ^68. 


THE  BOUZEY  DAM. 


215 


people,  although  warned  of  their  danger.      It  is  stated  that  the 
stone  employed  was  not  homogeneous,  that  the  sand  was  too 


T.-.S 


HABRA  DAM 
FIG.   102. 

fine,  and  that  the  lime,  madeTdn  the  ground,  lacked  hydraulic 
activity. 


FIG.  103. 

The  Bouzey  Dam,*  Fig.  103,  was  situated  near  Epinal  in 
the  valley  of  the  Aviere  in  France,  being  intended  for  the 
supply  of  the  Eastern  Canal  (Canal  de  Test).  It  was  com- 

*  Genie  Civil,  vol.  xxvil.  p.  281. 


2l6  FAILURES  OF  HIGH  DAMS. 

menced  about  1878,  commenced  to  fill  in  November,  1881, 
with  a  capacity  of  some  250  million  cubic  feet.  It  was  built 
of  dressed  sandstone  laid  in  hydraulic-lime  mortar.  The 
specific  gravity  of  the  stone  was  about  2.  It  was  a  sandstone 
conglomerate  of  the  crushing  strength  of  295  to  550  tons  per 
square  foot.  The  dam  was  1700  feet  long,  resting  on  a  forma- 
tion of  the  new  red  sandstone,  which  was  fissured  and  per- 
meable. A  guard-wall,  at  the  up-stream  face  of  the  dam, 
reached  down  to  solid  rock.  On  the  I4th  of  March,  1884,* 
water  being  within  8  feet  of  full  height,  a  portion  of  the  dam 
4/^/1  feet  in  length  suddenly  assumed  a  curved  form,  being  some 
15  inches  out  of  line  at  the  centre,  though  still  remaining  ver- 
tical, and  there  was  a  sudden  increase  in .the  flow  of  springs 
below  the  dam.  In  1885  the  reservoir  was  emptied  and 
examinations  were  made.  It  was  found  that  the  dam  had 
separated  from  the  guard-wall.  Repairs  and  additions  were 
made  at  the  base  of  the  dam  as  indicated  in  the  figure,  in  which 
the  dotted  lines  represent  the  original  work.  The  base  was 
greatly  widened  and  carried  down  to  rock  as  shown.  In  1889 
the  sluices  were  closed  and  water  in  due  time  rose  to  full 
height.  The  dam  stood  till  April  27,  1895,  when,  the  water 
being  within  2  feet  of  the  top  of  the  dam,  a  portion  594  feet 
long  and  34  feet  deep  was  overturned.  The  fracture  was 
nearly  level  longitudinally.  Transversely  it  was  level  to  within 
some  1 3  inches  of  the  outer  face,  where  it  broke  off  when  the 
dam  tilted.  The  overturned  part  included  all  but  90  feet  of 
the  portion  originally  displaced.  About  100  people  were 
drowned  by  this  disaster.  This  was  a  case  of  dimensions 
carried  to  the  extreme  of  lightness,  the  dam  having  but  18  feet 
thickness  at  40  feet  below  the  top,  where  we  must  assume  that 
the  water  was  liable  to  stand.  Formula  (20),  taking  2  for  the 
specific  gravity,  would  call  for  a  thickness  of  28  feet.  It  is 
probable  that  the  dam  would  have  stood  had  the  bottom  been 
properly  secured  at  first. 

*  Inst.  Civil  Engineers,  vol.  cxxv.  p.  461. 


DAM  ACROSS    THE   COLORADO   RIVER.  2 1/ 

Although  a  wedge  1 3  inches  wide  broke  off  the  outer  edge 
of  the  dam,  it  cannot  be  affirmed  that  the  accident  resulted  from 
the  crushing  of  the  stone.  The  latter  was  merely  an  incident 
of  the  overturning.  When  the  entire  weight  of  the  detached 
portion  came  upon  the  outer  edge  of  the  standing  part  such  a 
result  was  unavoidable. 

This  accident  suggests  a  way  not  ordinarily  foreseen  in 
which  such  a  dam  may  fail.  We  will  suppose  that  in  the  course 
of  construction,  when  the  work  is  at  a  certain  uniform  height, 
the  contractor  practises  some  familiar  trick,  and  lays  an  entire 
course  of  the  work  with  worthless  cement,  or  that  the  work  is 
stopped  for  a  season,  and,  when  resumed,  the  succeeding  course 
is  not  bedded  in  mortar.  To  give  the  exposed  part  of  the  work 
a  good  appearance  he  carefully  fills  and  points  the  down- 
stream joints  with  good  cement.  The  water,  on  filling  of  the 
reservoir,  enters  the  defective  joint  freely,  but  is  stopped  on  the 
down-stream  edge.  The  consequence  is  that  the  superin- 
cumbent part  is  expOsecPltot  only  to  the  horizontal  pressure 
on  the  up-stream  side,  but  to  an  upward  pressure  on  the  bottom, 
more  than  doubling  the  destructive  forces  taken  account  of  in 
designing  the  dam. 

As  to  the  possibility  of  practising  such  a  fraud,  this  fact  is 
within  my  knowledge :  A  contractor  building  the  piers  of  an 
important  railroad  bridge  was  short  of  cement.  A  neighboring 
sand-pit  furnished  sand  very  similar  in  appearance  to  the 
cement  he  was  using.  He  gathered  his  empty  cement-barrels, 
took  them  in  the  night  to  the  pit,  filled,  headed,  and  returned 
them  to  the  work,  and,  mixing  the  contents  with  water  and 
ordinary  sand,  put  it  into  the  work  unquestioned  by  the 
inspectors. 

Dam  Across  the  Colorado  River  at  Austin,  Texas. — The 
failure  of  this  dam  having  occurred  in  April,  1900,  as  this 
writing  was  drawing  to  a  close,  some  notice  of  this  event 
appears  proper,  especially  as  the  writer  was  for  a  time  con- 
nected with  this  work  as  engineer.  Austin  is  the  capital  of  the 
State  of  Texas  and  had,  at  the  time  this  dam  was  commenced, 


21 8  FAILURES   OF  HIGH  DAMS. 

about  1 5  ooo  people.  The  river  and  dam  are  described  page 
104,  Fig.  52.  The  people  of  the  town  had  been  persuaded 
that  a  water-power  could  be  created  here  greatly  conducive  to 
their  prosperity,  and,  assuming  honest  and  competent  manage- 
ment, such  was  no  doubt  the  fact.  The  work  was  undertaken 
under  charge  of  a  board  of  works  consisting  of  eleven  mem- 
bers, with  the  mayor  as  chairman.  As  vacancies  were  not 
filled,  it  was  speedily  reduced  to  seven  or  eight.  The  writer 
examined  the  situation  in  March,  1890,  and  in  May  of  that 
year  was  appointed  engineer  of  the  board.  A  contract  was 
let  in  the  fall  of  1890  for  the  construction  of  the  dam  and  canal 
in  accordance  with  the  plans  of  the  engineer,  a  canal  being 
thought  necessary  to  reach  ground  suitable  for  the  pump-station, 
power-house,  and  expected  industrial  establishments.  The 
winter  of  1890-91  was  spent  in  the  construction  of  a  railroad 
and  in  excavating  for  the  canal  and  dam-site,  the  latter  requir- 
ing a  broad  and  deep  cut  through  the  bed  of  argillaceous  gravel 
which  filled  about  half  the  rock  canyon  of  the  stream  to  a  depth 
of  40  or  50  feet.  These  excavations  disclosed  some  unex- 
pected features.  The  escarpment  of  rock  against  which  the 
dam  abutted  on  the  east  side  rose  abruptly  to  a  height  of  50 
feet  or  more  above  low  water,  and  where  the  up-stream  face 
of  the  dam  met  it,  consisted  of  hard  firm  rock.  Near  the  toe 
of  the  dam  a  seam  cropped  out  some  2  or  3  feet  thick,  of 
extremely  pulverulent  material,  such  as  might  be  handled  with 
a  shovel.  This  was  perhaps  10  feet  above  low  water.  Above 
this  the  rock  was  sound  to  the  top,  with  this  exception:  the 
canal  excavation  disclosed  a  number  of  pockets  which  may  be 
described  as  vertical  holes  6  or  8  feet  diameter,  filled  with  a 
very  shelly  material  through  which  water  readily  disappeared. 
Elsewhere  the  rock  was  firm  and  impermeable,  puddles  of  rain- 
water standing  on  it  for  days  till  they  evaporated.  The  pro- 
cedure necessitated  by  this  feature  was  obvious  to  ordinary 
foresight,  viz.,  to  carefully  search  out,  excavate,  and  plug  up 
these  shelly  cavities,  and  to  dig  out  the  outcropping  seam  for 


DAM  ACROSS    THE   COLORADO   RIVER.  21$ 

3  or  4  feet  back  from  the  face  of  the  rock,  and  close  it  with 
masonry. 

In  the  second  place  the  rock  disclosed  by  the  excavation 
for  the  dam  was  less  firm  than  could  be  desired.  It  lay  in 
strata,  hard  and  soft.  There  seemed  to  be  no  advantage  in 
going  deeply  into  it.  It  was  decided  to  build  the  dam  as 
planned  and  later,  after  observing  the  action  of  the  water,  to 
extend  the  apron  with  a  bed  of  concrete. 

After  making  some  progress  with  the  masonry  other  alarm- 
ing symptoms,  though  not  of  a  physical  character,  disclosed 
themselves.  The  contractor  had  gained  such  a  footing  with 
the  chairman  and  members  of  the  board  that  no  efficient  con- 
trol by  the  engineer  was  possible.  No  hearing  could  be 
obtained  for  any  proposition  to  enforce  the  stipulations  of  the 
contract  by  law,  or  to  annul  the  same,  though  the  latter 
measure  was  strongly  urged.  It  became  apparent  that  a  first- 
class  or  even  a  tolerable  piece  of  work  could  not  be  expected. 
In  addition  to  this,  the  mayor"and  chairman  of  the  board  had 
developed  a  conspicuoustalent  as  a  hydraulic  engineer.  Tak- 
ing a  part  of  the  office  force  under  his  own  personal  direction, 
he  applied  himself  to  getting  up  a  different  plan  of  develop- 
ment, the  leading  feature  of  which  was  a  power-house  located 
close  to  the  toe  of  the  dam.  Experts,  so  called,  were  sum- 
moned to  confirm  the  chairman's  views,  and  performed  that 
duty  with  singular  unanimity  and  promptness,  receiving,  in 
each  case,  a  large  amount  of  profitable  employment  at  the 
city's  expense,  after  rendering  their  reports.  After  the  adop- 
tion of  this  project,  the  engineer,  fully  satisfied  that  a  successful 
issue  of  the  enterprise  under  such  control  was  impossible, 
resigned  his  position  and  disclaimed  all  further  responsibility 
for  the  work.  A  procession  of  engineers  in  charge  of  the  work 
followed  one  another  in  rapid  succession,  directed  and  con- 
trolled by  the  mayor  who  acted  under  the  nominal  advice  of 
one  of  the  aforementioned  experts.  In  finally  raising  the 
water,  it  found  its  way  through  one  of  the  above-mentioned 
pockets,  issued  below  the  dam,  and  washing  out  the  soft 


220  FAILURES  OF  HIGH  DAMS. 

stratum,  undermined  and  destroyed  the  head-gates  and  power- 
house, so  far  as  the  latter  was  completed,  occasioning  a  loss 
of  about  $100000.  This  accident  wrecked  the  enterprise 
financially,  as  it  destroyed  confidence  in  the  permanence  of  the 
works.  On  completion  of  the  power-house,  a  stream  of  water 
of  some  six  million  gallons  a  day  was  spouting  through  its 
foundations  and  continued  till  its  final  destruction. 

In  April,  1896,  the  author  wrote  to  the  then  mayor  of 
Austin  pointing  out  the  danger  to  the  dam  to  be  apprehended 
from  the  location  of  the  power-house :  first,  that  the  discharge 
of  the  wheels,  following  the  toe  of  the  dam  for  a  distance  of 
some  600  feet  before  reaching  the  open  river,  tended  directly 
to  destroy  the  footing  of  the  dam;  second,  that  it  tended 
indirectly  to  the  same  result  by  preventing  the  measures  of 
protection  originally  contemplated.  He  suggested  inquiry  and 
examination.  No  heed  was  given  to  this  warning.  A  well- 
known  citizen  of  Austin  states  that  he,  while  fishing  near  the 
dam  in  1897,  found  abrasion  so  far  advanced  that  he  ran  his 
fishing-rod  8  feet  under  the  toe.  T.  U.  Taylor,  Professor  of 
Engineering  in  the  State  University  at  Austin,  states  that,  in 
1899,  he  was  unable  to  reach  the  bottom  with  means  at  his 
command,  though  reaching  to  the  depth  of  10  feet  below 
ordinary  low  water.  To  any  one  comprehending  the  situation 
such  reports  should  have  struck  the  ear  like  the  cry  of  "  Fire !  " 
It  appears  that  no  official  notice  was  taken  of  the  matter.  In 
the  spring  of  1 899  a  flood  went  over  the  dam  fully  equal  to  that 
in  which  it  failed. 

On  the  7th  of  April,  1900,  with  10  or  1 1  feet  of  water 
going  over  the  dam,  a  portion  of  the  latter,  some  600  feet  in 
length,  parted  from  the  remainder  and  slid  down  the  stream, 
a  part  of  it  remaining  in  an  erect  position.  Under  the  sudden 
rush  of  water  the  power-house  collapsed  and  the  inmates,  eight 
in  number,  were  drowned. 

That  there  was  risk  and  hazard  in  doing  such  a  work  by 
contract  was  fully  realized;  but,  on  the  other  hand,  its  execu- 
tion by  day-labor  appeared  beset  with  great  difficulties,  since 


DAM  ACROSS    THE    COLORADO   RIVER.  221 

every  workman  would  have  had  his  backer  in  the  city  govern- 
ment, and  the  votes  of  workmen  in  city  elections  would  have 
been  made  contingent  upon  employment  at  high  wages  and 
light  work.  Weighing  these  difficulties  and  fully  counting  on 
the  efficient  support  of  the  board  of  works  in  the  event  of 
attempted  fraud,  the  engineer  gave  his  adhesion  to  the  principle 
of  contract  work. 

There  are  honorable  contractors ;  men  who  aim  to  do  their 
work  faithfully  and  to  acquire  the  confidence  of  the  community, 
and  who  do  not  bid  lower  prices  than  the  work  can  be  honestly 
done  for.  There  is  another  class  of  contractors ;  men  trained 
from  their  youth  in  deception,  trickery,  subornation,  perjury, 
and  every  villainous  instrumentality  of  fraud  that  can  suggest 
itself  to  the  mind  of  man.  A  work  of  this  kind  controlled  by 
men  entirely  inexperienced  in  such  matters,  is  very  apt  to  fall 
into  the  hands  of  a  man  of  the  latter  class :  one  who  underbids 
honest  contractors,  in  the  expectation  of  "beating  his  way" 
through  the  work.  In  suclTa^work  calling  for  at  least  50  ooo 
barrels  of  Portland  cement,  the  withholding  of  15  or  20 
thousand  barrels  is  of  itself  a  good  profit,  and  it  is  very  difficult 
for  the  engineer  to  convince  people  of  this  character  that  such 
a  proceeding  brings  the  safety  of  the  work  into  question. 
Assuming  such  men  to  be  honest  and  conscientious,  they 
usually  have  great  reluctance  to  undergo  the  delay  incident  to 
the  enforcement  of  legal  remedies,  and  in  the  hands,  of  a 
shrewd,  shameless,  persistent,  and  determined  knave,  will 
stand  much  imposition  before  nerving  themselves  to  such  a 
step.  Where  these  persons  are  not  honest,  but  are  in  the 
receipt  of  money  ffom  the  contractor,  either  directly  or  in  the 
guise  of  business  profits  or  professional  fees,  the  case  is  still 
more  hopeless.  When  bribery  is  confined  to  inspectors,  it  can 
usually  be  detected  by  an  intelligent  engineer.  Their  natural 
'demeanor  changes.  They  become  negligent  in  duty,  reticent 
and  evasive  in  communication.  Their  conduct  betrays  the 
influence  of  bribes  almost  as  readily  as  it  would  betray  the  in- 
fluence of  drink.  But  when  an  engineer  has  reason  to  believe 


222  FAILURES  OF  HIGH  DAMS. 

that  his  employers  are  defrauding  their  constituents  by  corrupt 
collusion  with  contractors,  his  only  alternative  is  to  abandon 
the  work  as  he  would  abandon  fire  and  pestilence. 

A  Reservoir  Flood.  — An  opportunity  *  occurred  in  India, 
a  few  years  ago,  to  deliberately  observe  the  bursting  of  a  reser- 
voir and  the  progress  of  the  flood  down  the  stream.  Early  in 
September,  1893,  the  river  Bireh  Ganga  was  completely 
blocked  by  a  landslide  near  Gohna  in  Garhwal,  in  latitude  30° 
22'  north,  longitude  79°  32'  east.  An  immense  mass  of  earth 
and  rock  slid  from  the  neighboring  hill  and  filled  the  valley  or 
the  stream  for  a  length  of  2  miles,  and,  rising  to  a  height  of 
800  feet  above  the  river-bed,  completely  stopped  the  flow  of  the 
stream,  with  a  drainage-area  of  90  square  miles,  so  that  nearly 
a  year  elapsed  before  the  water  raised  to  run  over  the  top. 
This  is  a  mountain  stream  with  a  slope  of  250  feet  to  the  mile. 
The  matter  came  in  charge  of  the  corps  of  engineers  for  India, 
who,  although  no  human  power  could  avert  the  final  catas- 
trophe, did  what  they  could  to  ameliorate  it.  They  erected 
telegraph-lines  to  warn  the  people,  and  placed  marks  to  show 
the  probable  height  of  the  flood  at  points  on  the  stream.  They 
dismantled  bridges  and  surveyed  the  future  lake,  which  when 
ready  to  overflow  had  a  capacity  of  16^  billions  of  cubic  feet. 

From  the  data  available,  necessarily  very  imperfect,  the 
engineers  assigned  May  15,  1894,  as  the  probable  date  of  the 
breach.  After  completing  the  survey  of  the  lake,  and  becom- 
ing better  acquainted  with  the  flow  of  the  stream,  the  date  was 
changed  to  August  15.  Telegraph-stations  were  established 
at  all  important  points,  and  warnings  were  disseminated  as  to 
the  condition  of  the  lake,  as,  that  the  breach  might  be  expected 
in  a  fortnight;  that  it  might  be  looked  for  in  48  hours;  that  it 
was  liable  to  occur  at  any  minute,  etc.  Early  in  August  the 
water  escaped  freely  by  percolation.  The  breach  occurred  at 
11.30  P.M.  on  the  25th.  At  4  A.M.  of  the  26th,  the  water  had 
fallen  390  feet  and  more  than  10  billions  of  cubic  feet  had 

*  Journal  of  the  Society  of  Arts,  London,  March,  1896,  p.  431. 


A    RESERVOIR   FLOOD.  22$ 

escaped.  The  water  rose  260  feet  above  normal  level  imme- 
diately below  the  dam,  160  feet  at  a  distance  of  13  miles,  and 
it  reached  that  height  at  the  latter  point  in  25  minutes  after  the 
rupture.  At  a  distance  of  20  miles  it  commenced  to  rise  in  47 
minutes ;  at  a  distance  of  30  miles  it  commenced  to  rise  in  80 
minutes,  and  reached  the  extreme  height  of  1 30  feet  in  2  hours 
1 5  minutes ;  5  I  miles  down  it  commenced  to  rise  in  2  hours  30 
minutes,  and  reached  the  maximum  height  of  140  feet  in 

4  hours    15   minutes;    72   miles  down  it   commenced  to  rise 
in  3  hours  45  minutes,  reached  maximum  height  of  42  feet  in 

5  hours   10  minutes;   150  miles  down,  commenced  to  rise  in 
9  hours  1 5  minutes,  reached  the  maximum  height  of  1 1  feet  in 
12   hours.      So  complete  were  the  arrangements    that    not  a 
single  life  was  lost  during  the  flood. 


CHAPTER   XII. 
CANALS,   GATES,   ETC. 

WHERE  water-power 'is  to  be  applied  directly  to  manufact- 
uring establishments,  a  canal  usually  leads  from  the  dam,  or 
from  the  pond  created  by  the  dam,  down-stream,  diverging 
from  the  shore  according  to  the  contour  of  the  ground  till  a 
sufficient  width  is  secured  to  admit  of  placing  the  mills  and 
their  appurtenances  so  that  water  can  be  drawn  from  the  canal 
and,  after  passing  the  wheels,  discharged  into  the  river.  The 
arrangement  is  substantially  the  same  where  a  general  power- 
house is  adopted  in  connection  with  electrical  transmission, 
except  that,  less  room  being  required,  a  shorter  canal  is  admis- 
sible. Often  it  occurs  that,  in  order  to  secure  the  entire  fall, 
the  canal  must  have  a  considerable  length  irrespective  of  the 
requirements  of  the  mills  for  room. 

The  dimensions  of  the  canal  are  to  be  fixed  with  reference 
to  the  quantity  of  water  to  be  conveyed  by  it  and  the  loss  of 
head  that  is  considered  admissible.  Many  considerations  go 
to  the  decision  of  these  two  questions.  The  application  to  be 
made  of  the  power  determines  the  quantity  of  water  immediately 
required,  but  the  tendency  always  is  toward  a  progressively 
increased  use  of  water;  and  it  is  usually  safe  to  assume  that 
the  ultimate  use  will  be  limited  only  by  the  capacity  of  the 
stream.  Except  in  the  rare  instances  in  which  reservoir 
capacity  exists  capable  of  reducing  the  flow  of  the  stream  to 
substantial  uniformity,  the  use  of  auxiliary  steam-power  must 
be  assumed.  As  the  requirement  for  power  increases,  more 
water  is  used  during  the  time  that  it  can  be  obtained,  using 
steam  at  other  times.  Should  the  requirements  continue  to 


WASTEWAY.  225 

increase  without  limit,  we  should  reach  a  condition  in  which 
the  benefit  derivable  from  an  increased  use  of  water  would  not 
pay  the  cost  and  maintenance  of  the  appliances  for  the  use  of 
it.  Probably  the  greatest  use  that  is  ever  made  of  water  for 
power  is  such  a  use  as  does  not  permit  it  to  run.  to  waste  more 
than  four  months  in  the  average  year.  The  ultimate  capacity 
of  the  canal  never  need  exceed  what  this  condition  would  call 
for.  It  is  not  always  necessary,  however,  to  construct  the 
canal  with  its  ultimate  capacity.  It  may  be  built  with  a  view 
to  future  enlargement,  although  the  acquisition  of  ground  for 
the  ultimate  dimensions  should  in  no  case  be  deferred.  The 
work  of  enlargement,  while  the  canal  is  in  use,  is  generally 
more  expensive  than  the  original  work,  but  the  saving  of 
interest  on  the  deferred  part  of  the  cost  generally  justifies  the 
increased  expense.  Where  steam-power  is  employed  the 
enlargement  is  not  inordinately  expensive.  This  proceeding 
is  sometimes  justifiable  on  other  grounds,  for  a  canal  running 
for  many  years  with  excessive  dimensions  usually  fills  up  and 
entails  large  expense  for  cleaning. 

As  to  the  loss  of  head,  or  slope  of  the  water-surface,  this 
depends  upon  the  velocity  of  the  water,  which  cannot  exceed 
the  limit  of  safety  for  the  bed  and  banks.  Where  the  latter 
are  in  rock  or  are  protected  by  side  walls  or  pavements,  the 
question  resolves  itself  into  one  of  relative  expense.  A  high 
velocity  implies  diminished  first  cost  and  increased  loss  of  head. 
Generally  the  limits  of  velocity  in  a  water-power  canal  are 
between  2  and  4  feet  per  second.  When  the  latter  limit  is 
exceeded  we  generally  find  the  loss  incident  to  diminished  head 
outweighing  the  gain  from  diminished  cost.  Of  late,  however, 
there  is  a  tendency  to  adopt  higher  velocities  and  to  diminish 
the  loss  of  head  by  a  smooth  lining. 

Wasteway. — In  a  long  canal  of  uniform  cross-section,  if 
the  efflux  is  suddenly  closed,  the  motion  of  the  w«ater  continues 
till  the  slope  of  the  surface  is  obliterated  and  the  water  comes 
to  a  uniform  level  throughout  the  entire  length.  If  the  influx 
is  arrested  at  the  same  time  as  the  efflux,  the  water  will  fall  at 


226  CANALS,  GATES,  ETC. 

the  upper  end  of  the  canal  as  much  as  it  rises  at  the  lower  end, 
viz.,  by  one-half  the  total  slope.  If  the  influx  is  not  arrested, 
the  water  throughout  the  entire  length  of  the  canal  will  rise  to 
the  level  of  the  pond.  These  are  the  statical  conditions,  taking 
no  account  of  the  momentum  of  the  water.  The  momentum 
of  the  water,  that  is,  its  tendency  to  continue  in  motion,  will 
cause  it  to  rise  considerably  higher  at  the  lower  end,  and  in 
order  to  avoid  the  necessity  of  raising  the  banks  to  a  great 
height  it  is  customary  to  introduce  a  wasteway  at  the  lower 
end.  This  is  usually  controlled  by  flashboards  which  are 
removed  when  the  wheels  stop  (see  Figs.  62  and  63).  Its 
capacity  is  such  as  to  pass  the  entire  flow  of  the  canal  without 
raising  the  water  to  a  dangerous  height.  In  considering  the 
necessity  for  a  wasteway,  we  must  always  contemplate  the  case 
of  the  efflux  suddenly  closed  while  the  influx  remains  open,  as 
such  a  case  is  always  liable  to  occur  and  might  lead  to  great 
damage  if  not  provided  for.  The  necessity  for  a  wasteway 
depends  upon  the  length  of  the  canal,  and  slope  and  conse- 
quent velocity  of  the  water.  If  its  cost  falls  short  of  the  cost 
of  giving  the  necessary  height  to  the  banks,  it  is  introduced ; 
otherwise  not. 

Ice. — In  a  long  canal  subject  to  considerable  fluctuations 
of  level,  ice  often  breaks  up  after  forming  to  considerable  thick- 
ness, and  accumulates  in  the  lower  part  of  the  canal  in  such 
quantities  as  to  occasion  great  inconvenience  if  not  sluiced 
away.  A  waste-weir  may  usually  be  utilized  for  this  purpose, 
but  an  iceway  is  often  necessary  where  a  wasteway  is  not 
required.  This  consists  of  a  passage  leading  from  the  canal  to 
the  river,  controlled  by  flashboards,  the  bottom  and  sides  well 
secured  from  abrasion,  and  having  a  platform  on  which  men 
can  stand  to  handle  the  flashboards  and  by  means  of  pike-poles 
prevent  the  ice  from  gorging.  After  ice  forms  on  a  canal  it  is 
advisable  to  subject  the  surface  to  as  little  variation  as  possible. 

Anchor-ice  or  mush-ice  is  often  very  troublesome  in  canals, 
races,  and  penstocks.  Ice  forms  in  water  as  minute  crystals 
which  rapidly  unite  when  permitted,  and  form  a  continuous 


GA  TES.  227 

sheet.  When  water  is  in  rapid  motion  this  union  cannot 
readily  take  place  and  the  ice  floats  as  a  mushy  aggregation. 
It  appears,  in  this  form,  to  have  a  higher  specific  gravity  than 
solid  ice  and  is  very  readily  immersed.  It  fills  the  water  to 
considerable  depths,  passes  through  racks,  and  is  very  trouble- 
some in  wheels.  The  Mississippi  at  St.  Paul  in  severe  winters 
is  sometimes  packed  to  the  bottom,  in  parts  of  the  channel, 
with  anchor-ice  formed  in  the  rapids  at  St.  'Anthony.  The 
condition  favorable  to  the  formation  of  anchor-ice  is  open 
water  in  violent  motion.  Where  this  exists  not  far  above  the 
intake  of  the  canal,  trouble  is  usually  experienced.  The  best 
guaranty  against  anchor-ice  is  a  large  mill-pond  flowing  out  all 
the  rapids,  together  with  canals  of  gentle  slope  and  moderate 
velocity,  which  close  readily  on  the  advent  of  cold  weather. 

Sluices. — Every  water-power  canal  should  be  provided 
with  sluices  for  drawing  off  the  water  for  repairs  and  for 
removal  of  deposits.  These  should  be  of  ample  size  and  placed 
at  different  points  in  the  length  of  the  canal,  as  the  time  for 
such  operations  is  usually  limited  and  cannot  be  wasted  in  wait- 
ing for  the  water  to  disappear.  The  time  required  to  empty  a 
canal  or  basin  bounded  by  vertical  walls  through  an  orifice  in 
the  bottom  is  twice  that  required  to  discharge  an  equal  volume 
of  water  at  the  initial  rate  of  flow. 

GATES. 

.The  most  universally  applicable,  manageable,  and  reli- 
able gate  is  one  moving  straight  up  and  down  under  the 
action  of  force  sufficient  to  overcome  the  friction.  We  will 
first  consider  this  class  of  gates,  and  afterwards  the  modifica- 
tions required  by  special  conditions.  Large  gates  for  canals 
and  sluices  are  usually  made  of  heavy  plank  or  timber.  There 
are  two  modes  of  uniting  the  plank,  each  of  which  has  its  ad- 
vantages. Fig.  104  is  the  simplest  method  wherein  the  plank, 
cut  to  the  right  length,  are  placed  edge  to  edge  and  fastened 
together  by  long  iron  rods  with  heads  and  nuts.  These  latter, 


228 


CANALS,   GATES,  ETC. 


being  sharply  screwed  up,  unite  the  plank  into  a  single  piece 
fitting  closely  on  its  seat  and  free  from  leakage. 

When  a  gate  is  closed  but  seldom,  like  the  head-gates  of 
water-wheels,  or  guard-gates  designed  to  be  closed  only  in 
time  of  high  water,  the  seat  can  be  cut  in  the  stonework,  as 
at  b,  Fig.  104.  For  a  gate  liable  to  frequent  use,  the  wood 
sliding  on  stone  wears  too  rapidly,  and  it  slides  on  a  metallic 
seat  as  at  c.  The  wood  may  also  be  protected  from  wear  by 
a  metallic  strip  confined  by  countersunk  bolts.  A  gate  put 


FIG.  104^.  FIG. 

together  with  long  rods  lends  itself  very  readily  to  arrangements 
for  lifting  by  hydraulic  pressure,  as  indicated  by  Fig.  104, 
where  R  may  be  taken  as  the  piston-rod  of  a  hydraulic  cylinder 


GA  T£S. 


229 


standing  high  above  the  gate.  It  is  not  always  that  sufficient 
room  can  be  obtained  for  the  hydraulic  cylinder,  and  this 
arrangement  is  often  inadmissible  for  other  reasons.  Neither 
is  it  advisable  except  in  the  case  of  the  heaviest  gates  which 
require  to  be  lifted  against  the  full  pressure  of  the  water.  Fig. 
105  represents  a  common  form  of  gearing  for  lifting  wide  gates. 


- 

• 

E 

B 

fcdfb 

o 
0 

•         < 

r-  \ 

\@ 

\w 

11 

^1        ifll 

0 
0 
0 

( 

* 

1 

FIG.  105. 


FIG. 


FIG.  io5«. 


On  each  edge  of  the  gate  G  is  a  toothed  rack  operated  by  a 
pinion  D.  The  pinions  are  moved  by  worm-wheels  B  on  the 
shaft  F.  At  each  end  of  the  shaft  there  is  a  hand-wheel  E,  an 
arrangement  which  allows  four  men,  if  necessary,  to  work  at 
opening  the  gate.  The  gearing  is  supported  by  two  iron 
stands  A  bolted  to  the  masonry.  Gates  of  the  width  indicated 
at  Fig.  105,  operated  in  this  manner,  are  not  usually  raised  or 
lowered  under  full  pressure.  They  usually  close  basins  of 
small  capacity  like  the  forebays  and  penstocks  of  turbine- 
wheels.  They  are  provided  with  wickets  whereby  the  basin 


230 


CANALS,  GATES,  ETC. 


can  be  filled,  relieving  the  gate  wholly  of  pressure.  Then  the 
only  resistance  to  the  raising  of  the  gate  is  its  weight. 

Counterweight.  —  There  is  sometimes  an  advantage  in 
attaching  a  counterweight  to  a  gate,  consisting  of  one  or  two 
heavy  blocks  of  stone  attached  to  the  gate  by  chains  which 
pass  over  pulleys  above.  The  head-gates  of  canals  are  obliged 
to  be  lifted  under  full  pressure.  The  starting  of  the  gate  is  the 
4  '  pinch,  '  '  and  this  is  greatly  aided  by  a  counterweight.  There 
is  no  frictional  resistance  to  closing,  and  the  raising  of  the 
counterweight  does  not  bring  so  great  a  strain  upon  the  gearing 
as  the  raising  of  the  gate.  The  size  of  the  weights  should 
of  course  be  such  as  not  to  bring  any  greater  strain  upon  the 
gearing  in  lowering  than  in  raising. 

The  attachment  of  a  heavy  channel  of  cast  iron  to  the  edge 
of  the  gate  reaching  from  top  to  bottom,  as  shown  in  Fig.  105, 
is  a  cumbrous  arrangement,  not  consistent  with  the  design  of 
the  gate,  as  it  prevents  the  tightening  in  case  of  the  shrinking 
of  the  plank.  For  a  gate  designed  to  be  relieved  of  pressure 
during  its  movement  there  is  no  reason  why  the  arrangement 
of  Fig.  1  06  could  not  be  adopted,  which  shows  the  pinion  of 


FIG.  106. 

iron  and  rack-teeth  of  wood,  the  latter  being  cut  in  the  ends 
of  the  gate-plank.  For  a  gate  not  less  than  6  inches  thick, 
made  of  wrhite  oak,  maple,  or  other  hard,  close-grained  wood, 
this  mode  of  construction  would  not  be  inconsistent  with  a 
considerable  pressure. 

Often  the  hoisting-gears  must  be  placed  high  above  the 
passage  or  culvert  to  be  closed  by  the  gate.  For  such  a  case 
Fig.  107  is  a  suitable  arrangement.  Two  wooden  stems  are 
united  to  the  gate  by  brackets  which  receive  the  heads  of  the 


CO  UNTER  WEIGHT. 


23I 


through-bolts,  and  to  these  stems  the  rack-segments  are  bolted. 
They  are  firmly  united  to  each  other  by  cross-pieces  and  braces 
not  shown.  In  such  a  situation  the  gate  must  form  a  tight  joint 
on  the  lintel  or  arch  of  the  culvert  as  well  as  on  its  own  seats. 
A  gate  of  this  construction  was  adopted  by  Mr.  James  B. 
Francis  in  his  design  for  the  gate-house  of  the  Mine  Run  Canal 
at  Nashua,  N.  H. 

.In  the  second  mode  of  putting  the  gate  together,  the 
planks,  instead  of  being  confined  by  through-bolts,  are  bolted 
to  one  or  two  upright  stems.  Fig.  108  shows  a  small  gate  of 


FIG.  107. 

this  construction,  designed  to  control  an  opening  through  a 
bulkhead  wall.  Two  beams  fastened  by  anchor-bolts  project 
over  the  wall,  forming  a  "  cat-head  "  which  sustains  the  hoist- 
ing-gear. This  consists  of  a  shaft  resting  in  bearings  on  the 
beams  and  sustaining  between  the  latter  a  spur-gear  which 
meshes  with  a  toothed  segment  on  the  gate-stem.  This  passes 
between  the  beams,  and  its  plain  face  bears  against  a  roller. 
One  end  of  the  shaft  sustains  a  capstan- wheel  to  be  operated 
by  a  lever;  the  other  a  ratchet-wheel  with  a  pawl.  The  gate 
slides  on  a  framework  of  timber  built  into  the  masonry  around 


232 


CANALS,  GATES,  ETC. 


the  opening.  The  gate  is  shown  with  a  projecting  lip  or  sill 
to  limit  its  downward  movement,  and  guides  to  hold  it  laterally, 
only  one  of  which  appears.  These  parts  are  sometimes  dis- 


FIG.  108. 


pensed  with,  but  their  omission  is  liable  to  lead  to  accidents  and 
derangement.  For  instance,  when  the  gate  is  down  it  is  held 
firmly  by  the  pressure  of  the  water,  and  the  pawl  is  liable  to 


CO  UNTER  WEIGHT. 


233 


be  out  of  place.  In  this  condition,  if  the  water  is  drawn  off 
from  the  basin  supplying  the  opening,  the  gate  is  liable  to  drop 
out  of  its  connections.  In  this  construction  the  planks  are 


FIG.  109. 

tongued  and  grooved,  but  this  does  not  prevent  leakage  at  the 
ends  of  the  plank  should  there  be  any  shrinkage.  Head-gates 
sometimes  stand  open  for  weeks  and  months  and  are  liable  to 


234 


CANALS,  GATES,  ETC. 


shrink.  When  closed  down  in  case  of  accident  a  slight  leakage 
is  objectionable.  The  toothed  rack  cannot,  in  this  case,  be 
confined  to  the  stem  by  screw-bolts  unless  the  nuts  are  deeply 
countersunk  to  avoid  the  roller.  They  are  shown  as  confined 
by  heavy  split-head  lag-screws  which  are  almost  as  efficient  as 
screw-bolts. 

Gates  working  up  and  down  are  sometimes  objectionable  for 
extraneous  reasons.  The  necessary  head-room  is  not  always 
obtainable,  and  they  sometimes  are  objectionable  as  masking 
windows  and  obstructing  light  when  raised,  as  in  the  case  of  head- 
gates  they  necessarily  are  while  works  are  running.  In  such 


case,  the  best  substitute  is  a  gate  turning  on  a  vertical  spindle. 
Such  a  gate  when  open  presents  its  edge  to  the  current,  and  ob- 
structs the  opening  by  the  diameter  of  the  spindle.  It  is  operated 
with  less  force  than  the  sliding  gate,  but  is  generally  liable  to 
greater  leakage.  This  form  of  gate,  necessarily  made  of  iron,  is 
shown  in  horizontal  outline  at  Fig.  1 10,  in  vertical  elevation  at 
Fig.  in.  It  consists  of  a  plate  united  to  a  strong  hollow  spindle 


CO  UN  TER  WEIGHT. 


235 


and  stiffened  by  ribs.  A  plate  extends  across  the  culvert  at  the 
bottom  and  is  confined  by  being  built  into  the  concrete  floor. 
It  contains  the  socket  or  seat  for  the  foot  of  the  spindle.  A 
similar  plate  spans  the  culvert  at  the  top,  containing  an  eye  for 
the  passage  of  the  spindle,  and  a  broad  flange  or  web  built  into 
the  masonry  of  the  arch-covering.  These  two  plates  carry  the 
projecting  lips  or  seats  against  which  the  web  of  the  gate 
closes.  They  are  also  formed  to  unite  with  two  vertical  plates 
which  extend  up  the  sides  of  the  culvert  and  are  built  into  the 
masonry  of  the  side  walls.  The  entire  frame  could  be  made 


FIG.  in. 

in  one  piece,  but  this  is  usually  hazardous  on  account  of  the 
liability  of  such  work  to  break  in  handling.  For  the  highest 
degree  of  accuracy,  all  the  surfaces  which  close  together  are 
faced  with  brass,  which  is  trimmed  and  scraped  to  a  close  fit 
after  the  work  is  set  up.  The  spindle  reaches  above  the  top 
of  the  masonry  and  is  fitted  with  a  worm-gear  for  operating 
the  gate.  For  wider  openings  these  gates  are  often  arranged 
in  pairs,  each  having  its  own  spindle  and  worm-gear  and  both 
worked  by  the  same  hand-wheel.  Fig.  112  shows  a  pair  of 
such  gates  with  separate  hand-wheels.  The  only  resistance 
to  movement  offered  by  these  gates  being  the  friction  on  the 
spindle,  it  is  never  worth  while  to  adapt  them  to  working  by 
power.  Such  a  gate  is  very  liable  to  obstruction  from  gravel 
and  small  stones  which  get  pinched  between  the  closing  sur- 


230  CANALS,  GATES,  ETC. 

faces.  Such  stones  commonly  gain  access  to  the  culvert  by 
rolling  on  the  bottom,  and  may  be  excluded  by  forming  a 
pocket  in  the  bottom  of  the  culvert  into  which  the  stones  fall 
and  from  which  they  may  be  removed  from  time  to  time. 

Gates  working  under  great  pressure  and  gates  liable  to 
frequent  closing  are  often  arranged  so  as  not  to  slide  on  their 


FIG.  112. 

closing  surfaces.      The  latter  are  inclined  to  the  line  of  motion 
of  the  gate,  and  are  in  contact  only  when  the  gate  is  closed. 


FIG.  113. 

This  arrangement  is  indicated  by  Fig.  1.13,  in  which  the  gate 
slides  upon  the  guide  AD.  The  closing  surfaces  are  AB  and 
CF,  which  do  not  touch  each  other  except  when  the  gate  is 
closed.  In  this  disposition  there  is  no  wear  upon  the  contact 


GA  TE-HO  USES.  237 

surfaces,  and  these  can  be  adjusted  with  all  possible  nicety, 
without  liability  to  derangement  from  use.  Gates  in  pipes 
where  the  pressure  is  liable  to  be  alternately  in  opposite  direc- 
tions have  two  closing  surfaces  and  fit  as  a  plug  or  wedge 
between  two  inclined  seats. 

We  refrain  from  entering  into  the  many  ingenious  forms  of 
gate  which  have  been  brought  forward  in  recent  years :  gates 
•designed  to  run  on  wheels,  with  devices  for  throwing  the 
pressure  upon  the  wheels  when  in  motion,  and  upon  the  seats 
when  at  rest ;  gates  with  friction-rollers ;  cylindrical  gates 
moved  by  turning  on  radius  bars ;  gates  attached  to  radius 
bars  which  can  be  raised  and  lowered  by  slightly  changing 
their  inclination  to  the  same,  etc.,  etc.  All  these  find  appli- 
cation in  special  cases,  but  they  usually  involve  complications 
in  the  construction  of  the  masonry  which  more  than  offset  their 
ease  of  manipulation. 

Gate-houses. — The  influx  to  an  important  water-power 
canal  is  usually  controlled  by  a  gate-house,  consisting  of  a 
series  of  gates,  with  their  hoisting-gear,  enclosed  in  a  building 
and  covered  by  a  roof.  Fig  114  represents  a  gate-house 
designed  by  the  author  in  a  project  for  development  of  water- 
power  at  the  Great  Falls  of  the  Potomac  near  Washington, 
D.C.  The  water-passages  consist  of  twelve  6-foot  sluices 
separated  by  2-foot  piers,  and  controlled  by  gates  of  the  form 
shown  in  Fig.  104.  The  gates  are  supposed  to  be  moved  by 
hydraulic  pressure,  a  cylinder,  with  piston  and  rod,  standing 
over  each  gate.  The  gate  is  raised  by  admitting  water,  under 
pressure,  below  the  piston  and  allowing  it  to  escape  above,  and 
lowered  by  the  reverse  process.  Where  water,  under  sufficient 
pressure,  can  be  obtained,  as,  for  instance,  from  the  water- 
mains  of  a  town,  this  is  unquestionably  the  simplest  mode  of 
operating  heavy  gates.  It  .is  even  preferable  in  most  cases 
where  the  power  has  to  be  generated  by  a  special  water-wheel 
at  or  near  the  gate-house,  a  pipe  for  conveying  the  water  being 
so  much  simpler  than  the  ordinary  connection  by  shafting. 


CANALS,  GATES,  ETC. 


RA  CKS. 


239 


Squaring-shaft. — A  device  called  a  squaring-shaft  is  some- 
times applied  to  gates  operated  by  hydraulic  pressure.  Its 
purpose  is  to  prevent  the  gate  from  getting  out  of  line  in  its 
movement  and  thus  pinching  or  binding  between  its  guides, 
which  it  is  thought  liable  to  do  on  account  of  the  power  being 
applied  at  a  single  point.  This  consists  of  a  shaft  turning  in 
bearings  attached  to  the  masonry,  and  connected  with  the  gate 


FIG.  115. 

by  two  spur-pinions  gearing  with  two  toothed  racks  on  the  back 
of  the  gate,  as  indicated  at  Fig.   115. 

Racks. — The  piers  supporting  the  gate-house,  Fig.  114, 
are  prolonged  a  few  feet  up-stream  from  the  house,  and  sustain 
a  platform  and  the  racks  for  excluding  floating  bodies  from  the 
canal.  This  feature  is  not  always  introduced  at  gate-houses. 
It  is  in  fact  more  commonly  omitted,  and  floating  bodies 
allowed  freely  to  pass  the  sluices  and  lodge  upon  the  racks 
appertinent  to  the  different  wheels.  This  course  is  pursued 
where  the  water  is  supplied  to  different  lessees  by  a  separate 
company  or  owner,  who  is  under  no  legal  obligation  to  exclude 
floating  matters  and  prefers  to  throw  that  labor  upon  the 
lessees.  Where  the  water-power  is  owned  and  used  by  the 
same  party  it  is  a  question  of  relative  economy  whether  the 
debris  should  be  excluded  at  the  influx  or  efflux  of  the  canal. 
In  certain  seasons  of  the  year,  especially  in  time  of  falling 
leaves,  great  quantities  of  trash  have  to  be  raked  out  of  the 
racks  and  sluiced  back  into  the  river.  The  head  of  the  canal 


240  CANALS,   GATES,  ETC. 

often  offers  better  facilities  for  this  latter  operation  than  the 
wheel-racks.  The  racks  consist  of  flat  iron  bars  about  4  inches 
wide  and  \  inch  thick,  spaced  about  eight  to  the  foot.  These 
are  usually  obtainable  from  makers  in  sections  containing  16 
or  20  bars  each.  Otherwise  they  can  be  inserted  in  a  slotted 
plate  at  the  bottom  and  supported  by  a  notched  plate  at  the 
top  and,  if  necessary,  at  intermediate  points,  being  fastened  by 
keys  at  the  top.  They  have  to  be  strongly  supported,  as  the 
rack  is  liable  to  become  so  obstructed  by  trash  that  the  canal 
becomes  empty  and  leaves  the  rack  acting  as  a  dam.  They 
must  nevertheless  be  supported  in  such  a  way  as  will  not  inter- 
fere with  the  rake  used  in  removing  trash. 


CHAPTER    XIII. 
HYDRAULIC  MOTORS.     WATER-WHEELS, 

THE  energy  of  falling  water  may  be  applied  to  the  propul- 
sion of  machinery  in  different  ways.  An  oscillatory  motion 
may  be  secured  by  a  lever  turning  on  a  joint  at  the  middle  and 
carrying  a  vessel  at  each  end,  the  amplitude  of  the  oscillation 
of  the  vessel  corresponding  to  the  fall  of  water.  When  the 
empty  vessel  reaches  its  full  height  it  automatically  opens  a 
valve  and  fills  with  water;  at  the  same  time  the  full  vessel 
reaches  its  lowest  position  and  automatically  opens  a  valve 
which  empties  it.  Then  the  full  vessel  descends  and  the  empty 
one  rises,  etc. 

Water  flowing  through  a  long  pipe  is  alternately  brought 
to  rest  and  set  in  rapid  motion  by  the  automatic  action  of 
valves.  The  momentum  of  the  arrested  mass  causes  it,  while 
coming  to  rest,  to  exert  a  pressure  greatly  in  excess  of  that 
due  the  head,  and  the  expenditure  of  a  large  quantity  of  water 
under  a  small  head  is  thus  enabled  to  raise  a  small  quantity 
to  a  great  height. 

By  a  recent  invention,  water  from  the  upper  pool  of  a  mill 
privilege  passes  down  through  a  vertical  shaft  sunk  in  the 
earth ;  turns  at  a  right  angle  and  pursues  its  course,  for  some 
distance  horizontally;  then  ascends  and  discharges  into  the 
lower  pool.  It  carries  down  air  in  the  form  of  minute  bubbles. 
In  the  horizontal  part  of  its  journey  the  air  rises  to  the  top  of 
the  passage,  and  accumulates  under  the  full  pressure  due  to  the 
depth  below  the  lower  pool  in  a  chamber,  whence  it  can  be 
drawn  for  use  in  driving  machinery. 

241 


242  HYDRAULIC  MOTORS, 

By  far  the  most  common  mode  of  utilizing  the  energy  of 
falling  water  is  by  causing  it  to  act  directly  upon  organs 
attached  to  a  rotating  shaft,  which  combination  is  called  a 
water-wheel.  Water  acts  to  rotate  a  shaft  in  three  ways: 
(i)  by  weight,  (2)  by  impulse,  (3)  by  reaction.  Few  wheels 
act  wholly  by  either  of  these  modes,  but  wheels  take  different 
forms  according  as  one  or  other  of  these  modes  of  action  pre- 
ponderates. 

Water-wheels. — Although  this  term  is  properly  applied  to- 
all  hydraulic  motors  that  rotate,  there  is  a  convenience  in 
restricting  it  to  such  wheels  as  act  mainly  by  the  weight  of  the 
water,  turn  on  horizontal  shafts,  and  move  with  a  low  velocity, 
a  velocity  that  has  no  necessary  relation  to  the  head  under 
which  the  wheel  works.  We  will  here  use  it  in  this  sense, 
reserving  the  term  Turbine  for  wheels  on  which  the  water  acts 
mainly  by  impulse  or  reaction  and  which  move  with  a  velocity 
having  a  definite  relation  to  the  head.  These  wheels  are 
designated  as  overshot,  undershot,  or  breast  wheels  according 
as  they  receive  the  water  at  or  near  the  top,  below  the  centre, 
or  below  the  top  and  above  the  centre,  running  in  the  contrary 
direction  to  the  overshot. 

Figs.  1 1 6  and  1 17  represent  the  old-fashioned  breast- wheel, 
very  common  in  New  England  in  the  early  part  of  the  present 
century.  It  was  not  till  near  1850  that  it  began  to  be  replaced 
by  the  turbine.  It  consisted  of  a  circular  drum  of  a  diameter 
nearly  equal  to  the  head,  bearing  on  its  periphery  a  series  of 
vessels  called  buckets.  The  earlier  forms  were  made  wholly 
of  timber,  but  later  the  shafts  were  of  cast  iron,  together  with 
the  hubs  or  rosettes,  as  they  were  called,  which  sustain  the 
radial  arms.  These  rosettes  were  placed  at  intervals  of  about 
6  feet  on  the  shaft  and  this  interval  determines  the  length  of 
the  buckets.  To  the  outer  ends  of  the  arms  are  attached  a 
series  of  pieces  corresponding  to  what  are  called  "fellows  "  in 
ordinary  carriage-wheels,  which  constitute  the  "shrouding" 
and  form  the  ends  of  the  buckets.  The  sheathing  is  bolted  to 
the  inside  of  the  shrouding  and  forms  the  bottoms  of  the 


WA  TER-  WHEELS. 


243 


244 


HYDRAULIC  MOTORS. 


buckets.  To  the  end  circle  of  the  shrouding  is  attached  the 
series  of  toothed  segments  which  transmit  the  power  to  a  small 
pinion.  This,  in  turn,  gives  motion  to  a  shaft  carrying  a  large 
pulley  which  delivers  the  power  by  means  of  a  belt,  at  a  rate 
of  speed  suited  to  the  requirements  of  the  manufacture.  A 

BREAST  WHEEL  OF  LATER  CONSTRUCTION. 
LONGITUDINAL  SECTION. 


o: 


FIG.  117. 


FIG.  117*.  FIG.  117$. 

series  of  beams,  Fig.  n6a,  extends  across  the  channel  of 
approach,  called  the  flume,  in  front  of  the  wheel  and  just  clear- 
ing the  buckets,  forming,  by  the  interstices  between  them,  the 
passages  of  admission  to  the  wheel.  These  passages  are  con- 
trolled by  gates  A,  B,  called  wicket-gates,  each  consisting  of  a 
plank  which  slides  on  the  top  of  a  beam  and  closes  against  the 
vertical  face  of  the  adjacent  beam.  These  gates  are  moved  by 
rods  connecting  them  with  a  series  of  arms  on  a  rocking  shaft 


WA  TEK-  WHEELS.  2^ 

C  which  extends  across  the  flume  and  receives  a  rocking- 
movement  from  the  regulator  of  the  wheel.  Below  the  gates 
is  a  "breast,"  viz.,  a  concave  cylindrical  surface  of  planking 
concentric  with  the  wheel,  and  as  close  to  the  same  as  is  con- 
sistent with  movement.  This  prevents  the  water  from  spilling 
out  of  the  buckets  till  it  has  reached  the  lower  level.  Fig.  1 17 
shows  a  longitudinal  section  of  a  similar  wheel,  and  Fig.  118 
indicates  a  different  mode  of  admitting  the  water.  The  influx 
openings  are  controlled  by  rolling  and  unrolling  a  sheet  of 


FIG.  '118. 


stout  canvas  or  gutta  percha,  so  as  to  cover  and  uncover  them 
according  to  the  requirements  of  the  wheel. 

We  may  notice  some  of  the  more  obvious  losses  of  effect 
incident  to  this  form  of  wheel.  It  is  often  convenient  in  com- 
putations relative  to  the  efficiency  of  water-wheels  to  regard 
the  energy  as  represented  by  the  head,  and  any  loss  of  head 
as  representing  a  proportional  loss  of  energy.  First,  there  is 
a  loss  at  the  entrance  to  the  wheel.  In  a  wheel  acting  on  a 
head  of,  say,  18  feet  the  water  enters  under  an  average  head  of 
perhaps  4  feet  and  reaches  the  partly  filled  buckets  with  a 


246  HYDRAULIC  MOTORS. 

velocity  of  some  16  feet  per  second.  The  periphery  of  the 
wheel  moves  with  a  velocity  of  6  to  8  feet  per  second,  say 
7  feet.  Here  we  undergo  a  loss  of  the  head  due  to  a  velocity 
of  1 6 —  7  =  9  feet  per  second,  viz.,  1.3  feet.  The  water 
escapes  from  the  wheel  with  a  velocity  of  7  feet  per  second,  and 
the  energy  due  to  this  velocity  is  ineffective  upon  the  wheel, 
involving  a  loss  of  0.75  feet.  Again,  the  wheel  cannot  be 
placed  with  its  lowest  point  exactly  at  the  level  of  low  water. 
The  water  is  above  the  point  of  low  water  for  a  large  part  of 
the  year,  and  the  wheel  must  be  so  placed  as  not  to  undergo 
too  much  obstruction  from  backwater.  For  this  reason  the 
wheel  cannot  be  placed  less  than  a  foot  above  the  lowest  level 
of  the  water.  Finally,  there  is  the  loss  incident  to  the  escape 
of  water  between  the  buckets  and  the  breast,  which,  in  the 
ordinary  running  of  the  wheel  and  working  condition  of  the 
buckets,  may  readily  amount  to  10  per  cent  of  the  total  power. 

This  form  of  wheel  is  so  nearly  obsolete  that,  considered  as 
a  motor,  hardly  anything  more  than  a  historical  interest 
attaches  to  it.  There  is  one  aspect  in  which  it  often  has  a 
practical  interest  for  hydraulic  engineers.  Water  is  often  drawn 
under  grants  made  fifty  or  one  hundred  years  ago,  entitling  the 
user  to  so  much  water  as  is  necessary  to  drive  a  breast-wheel  of 
specified  dimensions.  Courts  hold  that  the  breast-wheel  is 
referred  to  merely  as  a  convenient  means  of  defining  the 
quantity  of  water  intended  to  be  granted,  and  that  this  quantity 
may  be  used  on  any  motor  whatever.  It  therefore  becomes 
necessary  to  secure  a  judicial  definition  of  the  quantity  of  water 
intended  to  be  granted,  expressed  in  cubic  feet  per  second. 
Such  proceedings  necessitate  intelligent  inquiries  as  to  the 
construction,  operation,  and  efficiency  of  the  particular  form  of 
wheel  referred  to  in  the  grant. 

Fig.  119  and  details  represent  an  old  form  of  undershot 
wheel,  made  entirely  of  wood, — such  a  wheel  as  used  to  be 
common  in  rural  grain-mills  of  European  countries.  It  is 
placed  outside  the  mill,  and  a  shaft  extends  through  the  wall, 
communicating  motion  to  the  machinery.  The  wheel  is  shown 


WA  TER-  WHEELS. 


247 


as  working  on  a  head  of  about  6  feet,  and  a  wheel  of  this  size 
would  use  not  over  10  cubic  feet  per  second.  The  water 
passes  the  wheel  in  a  rectangular  sluice  concentric  with  the 
wheel,  in  which  the  floats  revolve  with  as  little  clearance  as 
is  consistent  with  movement.  The  design  is  interesting  as 


FIG.  119. 

showing  the  methods  of  construction  adopted  in  these  old 
wheels.  The  shaft  is  a  round  log  some  30  inches  in  diameter — 
not  that  such  a  diameter  is  necessary  for  strength,  but  that  it  is 
convenient  for  securing  the  arms  of  the  wheel  as  well  as  those 
of  the  great  wooden  gear  which  drives  the  stones.  The  details 
b,  c,  dy  e,  f,  g,  h  show  the  mode  of  inserting  and  confining 


248 


HYDRAULIC  MOTORS. 


the  arms  in  the  shaft.  Three  elongated  slots  or  mortises  are 
cut  through  the  shaft  in  which  the  arms  are  inserted,  and  locked 
together  as  indicated.  The  first  is  only  wide  enough,  length- 
wise of  the  shaft,  to  insert  the  arm,  the  second  wider,  the  third 
wider  still.  When  the  arms  are  inserted  and  locked  together, 
the  widest  of  the  vacant  spaces  is  filled  with  a  wooden  wedge. 
Fig.  1 20  shows,  in  dotted  lines,  the  gudgeon  on  which  the 
wheel  runs.  It  appears  to  have  been 
pointed  or  wedge-shaped  and  driven  in. 
A  gudgeon  inserted  in  this  manner 
should  be  ragged  or  corrugated  to  avoid 
working  loose.  This  was  not  the  mode 
of  inserting  the  gudgeon  in  the  Ameri- 
can practice.  The  gudgeon  was  pris- 
matic in  shape,  or  perhaps  a  little 
larger  at  the  inner  end,  and  was  in- 
serted in  a  mortise  cut  from  the  outside. 
The  vacant  space,  after  inserting  the 
gudgeon,  was  filled  with  a  packing- 
piece,  and  this  was  tightly  confined  by 
bands  driven  on  hot.  After  applying 
the  bands,  small  iron  wedges  were 
driven  into  the  end  of  the  shaft  around 
the  gudgeon  to  fix  the  latter  more 
firmly,  i  and  k  show  the  form  of  the 
crown  segments  (shrouding),  and  the 
mode  of  inserting  the  float-arms  is 
shown  at  m,  n,  I.  The  feed-gate  does 
not  move  in  grooves,  but  merely  ex- 
tends from  side  to  side  of  the  channel, 
FlG-  I20>  and  is  held  against  the  pressure  of  the 

water  by  two  jointed  rods,  which  allow  it  to  be  raised  and  -low- 
ered with  very  little  friction,  though  admitting  of  some  leak- 
age. Such  a  gate  is  tightened  by  cutting  a  groove  in  the  end 
and  inserting  a  piece  of  stiff  rubber  pipe  which  bears  against 
the  wall  of  the  sluice.  The  water  should  be  admitted  to  such 


WA  TER-  WHEELS. 


249 


a  wheel  in  an  inclined  direction,  the  downward  component  of 
its  motion  being  equal  to  the  velocity  of  the  extremity  of  the 
float.  This  wheel  is  not  subject  to  the  same  loss  of  head  at 
the  influx  as  the  breast-wheel,  but  the  leakage  is  somewhat 
greater  in  proportion,  since  it  extends  all  around  the  perimeter 
of  the  float. 


FIG.  121. 

Fig.  121  shows  a  different  form  of  feed-gate  (often  called 
the  speed-gate)  with  inlet  openings  suited  to  a  head  of  10  feet 
or  thereabouts.  The  sluice  is  of  masonry,  and  the  wheel  and 
its  attachments  are  of  more  permanent  construction  than  in  the 
last  case.  The  shaft,  rosettes,  arms,  and  crown  segments  are 
-of  iron  together  with  the  float-arms ;  the  sheathing  and  floats 
being  of  wood.  It  will  be  noticed  that  the  water  enters  the 
in  an  inclined  direction,  the  vertical  component  of  its 


250 


HYDRAULIC  MOTORS. 


motion  being  about  equal  to  or  a  little  greater  than  the  velocity 
of  the  tip  of  the  float.  Should  the  water  enter  the  wheel  hori- 
zontally, every  float  would  strike  the  stream  with  great  force, 
accompanied  by  noise,  violent  strain  on  the  floats,  and  loss  of 
useful  effect.  The  gate  in  this  case  slides  in  a  groove,  closes 
the  passages  by  rising  and  opens  them  by  descending,  the 
lower  passages  being  the  last  to  be  uncovered.  This  is  a  more 
modern  form  of  wheel,  having  an  iron  shaft  and  iron  rosettes 
for  confining  the  arms. 

Fig.  122  represents  an  overshot  wheel  of  a  very  early  type, 
made  wholly  of  timber.      It  is  represented  half  in  section  and 


FIG.  122. 

half  in  elevation,  the  spout  which  conducts  the  water  to  the 
wheel  being  shown  in  section.  The  wheel  is  mounted  upon  a 
square  wooden  shaft  which  is  provided  with  gudgeons  and 
banded  in  the  ordinary  manner.  The  figure  contemplates  two 
sets  of  arms,  each  set  consisting  of  four  pieces  formed  as  at  a 
and  b,  locked  together  and  confined  to  the  shaft  by  wedges. 
The  shrouding,  it  will  be  noticed,  is  very  deep,  giving  much 
greater  depth  to  the  buckets  than  is  required  in  the  breast-wheel 
or  than  is  necessary  to  contain  the  water.  The  wheel  having' 
no  breast  to  restrain  the  escape  of  water,  this  arrangement  is 


WA  TER-  WHEELS. 


251 


necessary  in  order  to  prevent  the  water  from  spilling  out  of  the 
buckets  till  it  has  nearly  reathed  the  level  of  the  lower  pool. 

_ 


FIG.  123. 

Fig.  124  shows  a  similar  wheel  of  more  modern  construc- 
tion.     The  shaft  is  of  cast  iron.      The  arms  are  like  those  of 


FIG.  124. 

large  pulleys,  each  radiating  from  a  central  hub  which  is  keyed 
on  to  the  shaft.  Each  set  of  arms  carries  a  broad  web  or  ring 
which  corresponds  to  the  shrouding  in  a  wooden  wheel,  and 
forms  the  ends  of  the  buckets.  One  of  these  rings  is  toothed 
and  drives  a  pinion.  The  buckets  have  great  depth  for  the 
same  reason  as  in  the  preceding  case,  and  also  for  this  further 
reason :  the  water  enters  the  buckets  in  a  nearly  horizontal 


252 


HYDRAULIC  MOTORS. 


direction,  and,  to  avoid  a  shock  at  the  entrance,  the  extremity 
of  the  float  must  be  nearly  horizontal  at  the  point  where  the 


FIG.  125. 

water  enters.  The  floats  being  of  iron  can  conform  to  this  con- 
dition better  than  those  of  Fig.  122.  They  are  prolonged  by 
a  curve  till  they  are  nearly  tangent  to  the  exterior  circumfer- 
ence, i.e.,  nearly  horizontal  at  the  summit.  These  wheels  are 
suitable  for  a  fall  of  10  feet  and  are  intended  to  yield  about 
9  horse-power  on  that  head.  Wheels  of  this  description  have 
been  made  50  feet  in  diameter. 

Fig.  126  represents  a  wheel  which,  though  in  form  a 
water-wheel,  acts  in  some  degree  upon  the  principle  of  the  tur- 
bine. It  acts  to  but  slight  extent  by  the  direct  weight  of  the 
water,  and  it  gives  its  best  effect  with  a  peripheral  velocity, 
which  is  not  constant  for  all  diameters  like  that  of  the  ordinary 
water-wheel,  but  bears  a  definite  relation  to  that  due  the  head. 
The  water  entering  the  wheel  does  not  impinge  upon  a  flat 
vane  or  plunge  into  a  mass  of  water  in  a  bucket.  It  glides  up 
a  curved  vane,  comes  to  rest,  and  then  glides  smoothly  back 
and  escapes.  It  avoids  the  loss  at  the  entrance  which  is  in- 
separable from  all  the  forms  thus  far  considered,  and  it  avoids 
in  part  the  loss  at  the  discharge,  since  the  water  leaves  the 
wheel  in  a  direction  partly  contrary  to  that  of  the  wheel's 
motion,  and  the  quantity  of  energy  carried  away  in  the  dis- 
charge is  not  great.  The  wheel  is  shown  as  made  of  wood, 
though  such  a  wheel,  if  made  now,  would  probably  be  made 
of  iron.  The  shaft,  arms,  and  shrouding  are  put  together  as 


WA  TER-  WHEELS. 


253 


already  described.  The  floats  are  inserted  in  grooves  cut  in 
the  shrouding  and  are  firmly  confined  by  through-rods  which 
draw  the  two  sets  of  shrouding  together  and  grip  the  floats. 
Each  float  is  composed  of  several  plank,  and  is  stayed  at  the 
middle  by  an  iron  strap  bolted  to  the  back.  The  through-rods 


FIG.  126. 


cause  considerable  obstruction  to  the  water,  but  cannot  be 
avoided  in  a  wooden  wheel.  In  the  iron  wheel  they  can  be 
dispensed  with.  The  proper  position  for  these  rods  is  close  to 
the  back  of  the  float.  Situations  sometimes  offer  in  which  this 
wheel  may,  under  existing  conditions,  be  judiciously  applied, 
viz. ,  a  head  not  exceeding  6  feet,  and  an  application  not  call- 
ing for  a  high  velocity,  as  pumping,  grinding,  or  the  work 
incident  to  a  powder-mill.  The  best  speed  for  the  outer  ends 
of  the  floats  is  about  5  5  per  cent  of  that  with  which  the  water 
enters  the  wheel,  though  it  can  vary  from  50  to  60  without 


254 


HYDRAULIC  MOTORS. 


material  disadvantage.  The  diameter  of  the  wheel  is  three  or 
four  times  the  total  head.  The  best  efficiency  found  by  the 
earlier  experimenters  was  not  over  60  per  cent,  but  a  wheel  of 
this  form  erected  at  the  powder-mill  at  Angouleme  in  France, 
about  1847,  showed  an  efficiency  of  68  to  75  per  cent,  and  this 
efficiency  was  not  materially  diminished  by  a  considerable 
amount  of  backwater. 


SCALE  OF  FEE! 


FIG.  127. 


In  addition  to  the  losses  of  effect  already  pointed  out,  the 
disadvantages  of  water-wheels  as  compared  vvith  turbines  are 
very  great.  They  occupy  a  great  deal  more  room  than  tur- 
bines of  the  same  power,  and  must  be  enclosed  in  buildings  to 
prevent  obstruction  by  ice  in  winter.  Backwater  affects  them 
injuriously,  not  only  by  diminishing  the  head,  but  by  partly 
drowning  them  and  causing  them  to  expend  their  power  use- 
lessly in  ' '  wallowing, ' '  a  source  of  loss  from  which  turbines 
are  wholly  free.  The  necessarily  low  velocity  with  which  they 
move  necessitates  cumbrous  and  expensive  gearing  to  raise  the 
speed  to  the  requirements  of  industry,  which  is  constantly  call- 
ing for  increased  rates  of  speed.  These  numerous  disadvantages 


TURBINES,     GENERAL  PRINCIPLES.  255 

have  caused  the  water-wheel  to  be  almost  entirely  superseded 
by  the  turbine. 


TURBINES.       GENERAL    PRINCIPLES. 

We  come  now  to  consider  those  wheels  in  which  water  acts 
mainly  by  impulse  and  reaction,  and  which  run  with  a  velocity 
having  a  definite  relation  to  the  head. 

The  action  of  water  by  impulse  depends  upon  certain  well- 
Icnown  mechanical  principles.  Force  is  required  to  impart 
velocity  to  water,  and  the  velocity  imparted  is  a  true  measure 
of  the  force  exerted.  Thus,  if  we  find  water  issuing  from  an 
orifice  with  a  velocity  of  16.04  feet  P^r  second,  we  are  certain 
that  it  issues  under  a  head  of  4  feet.  When  water  is  in  motion, 
force  is  required  to  change  the  direction  or  velocity  of  its  motion, 
and  the  change  of  motion  is  a  true  measure  of  the  force. 
When  the  change  of  motion  is  due  to  the  action  of  a  vane  we 
know  that  the  pressure  of  the  vane  on  the  water  is  the  same  as 
the  pressure  of  the  water  on  the  vane.  Suppose  a  jet  of  water 


FIG.  128. 

moving  in  the  direction  DB,  Fig.  128,  with  the  velocity  AB, 
in  feet  per  second.  At  A  it  encounters  a  smooth  vane  which 
so  deflects  it  that  it  reaches  C  instead  of  B  at  the  end  of  one 
second.  It  glides  along  the  vane  and  glances  off  at  the 
extremity  with  undiminished  velocity,  AC  =  AB.  The  effect 
of  the  vane  is  to  impart  to  the  water  a  velocity  BC.  To  find 
the  pressure  of  the  water  on  the  vane,  which  is  equal  and 
opposite  to  that  of  the  vane  upon  the  water,  we  reason  thus: 
Gravity,  acting  freely  for  one  second,  would  impart  to  the 
water  a  velocity  of  g  feet  per  second.  The  pressure  of  the 


2$6  HYDRAULIC  MOTORS. 

vane  acting  for  one  second  imparts  to  it  a  velocity  of  BC  per 
second.  Therefore  the  pressure  on  the  vane  is  to  the  weight 
of  water  flowing  in  one  second  as  BC  to  g.  If  a  represent  the 
cross-section  of  the  stream,  and  w  the  weight  of  a  cubic  foot  of 
water,  the  weight  of  the  water  is  wav,  and  the  pressure  is 

BC 
wav pounds. 

o 

The  impulse  of  water  upon  a  stationary  vane  is  attended 
with  no  material  toss  of  energy.  The  water  glides  along  the 
vane  and  glances  off  at  the  extremity  in  a  direction  tangent  to 
the  latter  with  substantially  undiminished  velocity.  There  is 
in  fact  a  certain  friction  between  water  and  solids  which  has  to 
be  considered  where  large  surfaces  are  concerned,  but  in  these 
calculations  such  consideration  would  be  superfluous.  When 
the  vane  moves,  under  the  action  of  the  water,  a  portion  of  the 
energy  is  imparted  to  the  vane,  and  the  energy  of  the  stream 
is  correspondingly  diminished.  It  is  manifest  that  if  the  energy 
of  the  stream  is  wholly  imparted  to  the  vane,  it  must  leave  the 
latter  with  no  absolute  velocity.  That  is,  its  velocity  must  be 
equal  and  opposite  to  that  of  the  vane  at  the  point  of  exit. 

Let  us  now  consider  the  action  of  a  jet  on  a  flat  vane,  per- 


FIG.  129. 

pendicular  to  its  direction  and  moving  in  the  same  line.  In 
Fig.  1 29  let  BC  =  v  represent  the  original  direction  and 
velocity  of  the  jet.  BD  =  u,  the  velocity  of  the  vane.  Were 
the  vane  not  present,  a  particle  of  water  at  B  would  have 
reached  C  at  the  end  of  one  second.  By  the  action  of  the 


TURBINES.     GENERAL   PRINCIPLES.  2$? 

vane,  the  particle  finds  itself  at  the  point  A  at  the  end  of  one 
second,  DA  being  equal  to  v  —  21  =  DC.  A  C  is  the  change 
of  motion  due  to  the  action  of  the  vane,  and  the  pressure, 

AC 
regarded  as  parallel  to  AC,  is  wav  -  ;  but  the  change  of  motion 

normal  to  the  vane  is  DC,  and  the  normal  pressure  is 


DC  v  -u 

P  =  wav  -  =  wav  - 
g  g 


The  energy  imparted  to  the  vane  is 

f   ' (3I) 

This  expression  has  its  maximum  value  when  u  =  %v,  and 
becomes  in  that  case 

V* 

2or  *  \J     7 

h  being  the  head  to  which  the  velocity  is  due.  In  other  words, 
the  maximum  energy  that  can  be  imparted  to  a  flat  vane 
normal  to  the  stream  is  one -half  that  of  the  stream,  or  the 
maximum  efficiency  is  50  per  cent,  and  the  best  velocity  for 
such  a  vane  is  one-half  that  due  the  head. 

There  are  two  cases  in  which  the  energy  becomes  o,  viz.  : 

(1)  When  u  is  o,  i.e.,  when  the  vane  does  not  move.      In 
that  case,  by  eq.  (30), 

P  =  *wa^.  ......     (33) 

That  is,  the  pressure  on  the  vane  is  twice  that  of  the  head  to 
which  the  velocity  is  due. 

(2)  When  u  —  v,  i.e.,   when  the  velocity  of  the  vane  is 
equal  to  that  of  the  stream. 


258  HYDRAULIC  MOTORS. 

.  A  cup-shaped  vane,  Fig.  130,  reverses  the  direction  of  the 
water's  motion;   so  that,   if  such   a  vane   be    moving   in   the 
direction  of  the  stream  with  the  velocity  «, 
the  change  of  motion  will  be  2(v  —  u),  and 

^_^^  P  =  wav2^~U\     .      .      (34) 

FIG.  130.  ancj  tjie  energy  exerted  on  the  vane  is 

"  ~^-  •     '     (35) 


As  before,  the  expression  has  its  maximum  when  v  =  2u,  in 
which  case 

Pu  =  wav  —  =  wavh.  .      .      (36) 

2g  •  ^J 

Or,  the  total  energy  of  the  stream  is  imparted  to  the  vane,  and 
the  efficiency  is  100  per  cent.  We  have  proceeded,  however, 
upon  assumptions  which  cannot  be  perfectly  realized.  In  any 
practical  application,  the  direction  of  the  water's  motion  cannot 
be  exactly  reversed,  the  vanes  and  their  attachments  cannot 
move  without  friction,  the  water  cannot  approach  and  leave  the 
vanes  without  velocity  and  consequent  loss  of  head.  The 
practical  interpretation  of  this  result  is  that  floats  of  this  form 
are  consistent  with  the  highest  efficiency.  Equation  (34) 
shows  that  when  the  vane  does  not  move,  the  pressure 

t;2  t'3 

P  =  2iva  —  =  Axva  —  .....      (37) 


That  is,  the  pressure  on  the  vane  is  four  times  that  of  the  head 
to  which  the  velocity  is  due.  As  in  the  former  case,  the  energy 
is  o  when  u  =  o  and  when  u  =  v. 

To  trace  the  application  of  these  principles  to  different  forms 
of  vanes  and  to  vanes  which  do  not  move  in  the  same  line  as 
the  water,  would  be  out  of  place  in  a  practical  treatise.  We 
are  nevertheless  even  now  in  a  position  to  notice  two  points 


REACTION.  259 

of  importance  which  are  commonly  lost  sight  of  in  the  design 
of  turbines : 

1.  The  purpose  of  the  vanes  or  floats,  in  an  impulse-wheel, 
is,  to  effect  the  greatest  possible  change  in  the  motion  of  the 
water.      Their  length  need  be  no  greater  than  is  necessary  to 
accomplish  that  change. 

2.  It  is  a  condition  of  the  highest  efficiency  that  the  water 
should  leave  the  vane  in  a  direction  opposite  to  its  motion,  and 
with  a  velocity  equal  to  that  of  the  vane  at  the  point  of  exit. 
Where  the  edge  of  the  vane  is  radial  to  the  wheel,  different 
parts  of  it  move  with  different  velocities,  and  the  fulfilment  of 
this  condition  is  impossible. 

Reaction  is  the  pressure  exerted  on  the  walls  of  a  pipe  or 
vessel  from  which  water  is  discharged.  Strictly  speaking,  the 
discharge  of  water  from  a  pipe  or  vessel  does  not  create  pressure 
within  the  pipe  or  vessel  from  which  it  issues.  It  destroys  the 
equilibrium  of  pressures  previously  existing.  Suppose  the 
pipe,  Fig.  131,  filled  with  water  under  pressure,  and  free  to 
revolve  about  the  centre  C.  When  the  orifice  O  is  closed 


FIG.  131.  FIG.  1310. 

there  is  no  tendency  in  the  pipe  to  revolve.  The  water  presses 
equally  upon  every  part  of  the  interior,  and  the  force  tending  to 
turn  it  toward  the  right  is  exactly  balanced  by  that  tending  to 
turn  it  toward  the  left.  When  the  orifice  O  is  opened  the  con- 


26o  HYDRAULIC  MOTORS. 

ditions  are  changed.  There  is  now  a  small  area  on  one  side 
of  the  pipe  relieved  of  pressure,  while  the  pressure  acts  in  full 
force  on  the  other  side.  The  pipe  will  revolve  around  the 
centre  C  in  a  direction  opposite  that  of  the  stream. 

Suppose  the  stream  to  impinge  on  a  flat  vane  normal  to  its 
direction,  firmly  attached  to  the  pipe  and  in  a  plane  passing 
through  the  axis  of  rotation  (Fig.  131^).  The  water  will  escape 
radially  with  undiminished  energy.  A  constant  expenditure  of 
energy  would  be  necessary  to  cause  the  pipe  to  rotate,  because 
movement  of  the  orifice  would  increase  the  energy  of  the 
escaping  water.  The  stream  therefore  has  no  tendency  to 
rotate  the  pipe,  and  the  reaction  on  the  pipe  must  be  equal  to 
the  pressure  on  the  vane,  which  we  have  found  to  be  2wah. 

Let  Fig.  132  represent  the  rim  of  a  wheel  containing  the 
orifices  O  O,  so  disposed  as  to  discharge  water  in  a  direction, 


FIG.  132. 

as  nearly  as  may  be,  tangential  to  the  wheel.  We  assume  for 
our  present  purpose  that  the  direction  is  absolutely  tangential. 
Let  a,  as  before,  represent  the  cross-section  of  the  stream. 
The  water  is  supposed  to  be  at  a  greater  pressure  within  the 
wheel  than  without,  the  difference  of  pressure  being  represented 
by  the  head  //.  The  best  velocity  of  the  circumference  is  that 
with  which  the  water  issues,  being  the  velocity  due  the  head  //. 
In  this  case  the  absolute  tangential  velocity  of  the  water  leaving 
the  wheel  is  o.  The  energy  imparted  to  the  wheel  is  2wavli 
=  twice  the  energy  of  the  water  under  the  given  head. 

This  does  not  imply  that  the  wheel  is  capable  of  yielding 
an  efficiency  of  200  per  cent.  In  order  that  the  water  may 
issue  from  the  orifices  while  the  wheel  is  in  motion  it  must 


IMPULSE-   AND    REACTION- WHEELS.  26 1 

receive  a  tangential  velocity  equal  to  that  of  the  wheel,  and  to 
impart  this  velocity  requires  an  expenditure  of  energy  wavh. 
The  wheel  then,  under  the  conditions  supposed,  is  capable  of 
exerting  the  energy  2wavh  —  wavk  =  wavh,  and  from  this 
must  be  deducted  the  several  losses  incident  to  motion, 
together  with  that  due  the  deviation  of  the  issuing  stream  from 
the  direction  of  a  tangent.  We  here  ignore  the  centrifugal 
force  developed  in  the  water  by  its  rotation. 

Impulse-  and  Reaction- wheels. — Most  wheels  act  partly 
by  impulse  and  partly  by  reaction.  In  a  wheel  acting  purely 
by  impulse  the  water  issues  from  orifices  with  the  velocity  due 
the  head  and  impinges  upon  vanes.  In  a  purely  reaction- 
wheel  the  work  of  the  water  is  finished  when  it  issues  from  the 
orifices  of  discharge.  A  tangential  or  whirling  velocity  equal 
to  that  of  the  influx  orifice  is  imparted  to  the  water,  not  directly 
by  the  head,  but  indirectly  through  the  action  of  the  wheel. 
Neglecting  friction  and  losses  incident  to  the  movement  of  the 
water,  the  energy  imparted  to  the  wheel  by  the  water  is  twice 
that  corresponding  to  the  head  and  quantity  discharged,  but 
of  this  one-half  or  more  is  useless  energy,  being  that  expended 
in  imparting  the  necessary  tangential  movement  to  the  water. 

The  Pelton  or  Hurdy-gurdy  wheel,  to  be  described  later,  is 
an  impulse-wheel  pure  and  simple.  The  Barker  mill,  Fig. 
131,  and  the  forms  of  Figs.  132  and  133  are  reaction-wheels 


FIG.  133. 


pure  and  simple,  observing  that  in  Figs.  131  and  132  the 
orifices  of  influx  and  discharge  are  the  same.  All  wheels  with 
guide-vanes  may  be  regarded  as  acting  partly  by  impulse  and 


262  HYDRAULIC  MOTORS. 

partly  by  reaction.  The  tangential  velocity  of  influx  is  im- 
parted directly  by  the  head.  The  velocity  of  the  efflux  orifices 
is  less  than  that  due  the  head  and  greater  than  half  the  same. 
At  full  discharge  they  have  mainly  the  character  of  reaction- 
wheels  ;  at  diminished  discharge  more  the  character  of  impulse- 
wheels.  Impulse-wheels  and  reaction-wheels  have  this  in 
common :  their  efficiency  depends  upon  the  change  which  they 
effect  in  the  direction  of  the  water's  motion,  perfect  efficiency 
implying  exact  reversal.  Perfect  efficiency  also  requires  the 
water  to  leave  the  wheel  with  no  tangential  velocity,  a  condi- 
tion inconsistent  with  radial  orifices  of  discharge. 

Centrifugal  Force  playing  an  important  part  in  the  action 
of  turbines,  we  may  profitably  devote  a  few  words  to  that 
subject. 

A  mass  whose  weight  is  u>  revolving  around  a  fixed  point 
at  a  distance  r  therefrom  with  an  angular  velocity  GO,  tends 

to  depart  from  the  centre  of  rotation  with  a  force  —  o&r.    When 

the  body  moves  in  a  path  which  is  not  a  circle,  the  value  of  r 
at  any  particular  point  of  its  path  is  the  radius  of  curvature  at 
that  point.  When  the  size  of  the  body  is  great  compared  with 
r,  the  centrifugal  force  acts  with  different  intensities  at  different 
parts  of  it,  and  r  must  be  measured  to  the  centre  of  gravity  of 
the  body.  When  the  rotating  body  is  a  mass  of  liquid,  the 
pressure  within  the  same  increases  with  the  distance  from  the 
centre  of  rotation.  Consider  a  mass  of  liquid  rotating  around 
a  centre  lying  within  the  mass.  The  centrifugal  force  acting: 
on  a  cylindrical  film  whose  thickness  is  dr  and  area  unity  is, 
when  iv  is  taken  as  the  weight  of  a  cubic  foot  of  the  liquid, 

wdr 

— — o?V.     This  force  is  transmitted  to  all  the  films  lying  outside, 

<"> 

so  that  the  total  pressure  at  a  distance  rv  from  the  centre  is 


•    ,  .     9^Gtf  r  -co 

rdr  =  \r? =  w— .    .  f7g> 

1    g  *g 


CENTRIFUGAL  FORCE. 


263 


r^JO  is  the  velocity  at  the  distance  rl  from  the  centre  of  rotation, 

r*(*? 
and  -     -  is  the  head  due  that  velocity. 

Therefore  the  pressure  at  any  point  in 
the  whirling  mass  is  represented  by  the 
head  due  the  velocity  at  that  point.  This 
is  only  true  when  the  mass  extends  from 
the  centre  outwards.  The  pressure  ex- 
erted by  a  whirling  ring  of  water  whose 
internal  radius  is  rl  and  external  r2,  Fig. 
134,  is  represented  by 


FlG-  T34- 


•    (39) 


i.e.,  by  the  difference  between  the  head  due  the  velocity  at  r2 
and  that  at  rv 

When  the  ring  represents  a  turbine-wheel  with  water  flow- 
ing through  the  buckets,  it  is  manifest  that  equation  (39)  does 
not  hold,  because  while  the  wheel  is  moving  toward  the  right 
the  water  advances  toward  the  left  and  ca  does  not  represent 
the  angular  velocity  of  the  water.*  Errors  have  been  committed 
by  writers  on  the  turbine  in  failing  to  take  notice  of  this  fact. 

In  the  illustrations  of  the  principle  of  reaction  no  account 
is  taken  of  the  effect  of  centrifugal  force.  The  introduction  of 
this  element,  though  it  does  not  affect  the  principle,  makes  the 
problem  more  complex.  The  full  effect  of  centrifugal  force 
appears  in  the  arrangement  of  Fig.  131,  in  which  a  pipe  filled 
with  water  under  pressure  revolves  around  a  centre  C,  dis- 
charging from  an  orifice  O,  the  entire  mass  of  water  being  in 
rotation  with  uniform  angular  velocity.  The  pressure  acting  on 
the  orifice,  under  this  condition  will  be  2wah,  and  the  velocity 
of  discharge  will  increase  to  v  —  */2g  X  2.h  =  1.414  VTg-Ji. 
If  we  increase  the  velocity  «  of  the  orifice  so  as  to  make 
u=  1.414  V2gh,  we  develop  a  still  greater  centrifugal  force, 


*  See  Journal  of  the  Franklin  Institute,  vol.  cxvi.  p.  92. 


264  HYDRAULIC  MOTORS. 

and  so  on;  so  that  the  condition  of  maximum  efficiency 
v  =  —  u  is  impossible.  If,  for  example,  we  attempt  to  deter- 
mine the  value  of  u  on  the  asumption  that  it  is  equal  to  the 
velocity  with  which  the  water  issues  from  the  orifice  O,  we 
should  have  the  equation 


(40) 


or  i?  =  2gh  -f-  «2,  which  is  only  possible  when  h  =  O.  If, 
however,  we  load  the  machine  so  as  to  maintain  its  velocity 
at  that  due  the  head,  viz.,  u  =  V~2g/i,  we  should  have  for  the 
velocity  of  the  issuing  stream 


v  =  V2g/i  -f-  2gh  —  \'2gh  VX2,  .  •.  v  —  u  =  \/2gh(  t/2  —  i), 
and  the  loss  of  head,  which  represents  the  loss  of  power, 
=  i —  — -  =  //(  \'2  —  i)2  =  o.  1716^.  The  power  utilized, 

incidental  losses  excepted,  is  0.8284/1,  or  the  efficiency  is 
0.8284. 

If  we  put  the  velocity  n  =  2  \'2gh,  we  have  v  =  V2g/i  1/3, 
v  —  u  —  V2gli(  1/3  —  VV),  and  the  loss  of  head  is  h(  V  •$  —  4/2)* 
=  o.  ioi//,  and  the  efficiency  is  0.899.  The  practical  interpre- 
tation of  this  result  is  that  there  is  a  loss  of  1 7  per  cent  in  the 
first  case,  and  10  per  cent  in  the  second,  inherent  in  the  prin- 
ciple of  the  wheel.  With  higher  velocities  the  computation 
would  show  greater  economy,  and  with  an  infinite  velocity  we 
should  have  perfect  efficiency;  but  it  is  probable  that  with  any 
velocity  above  u  =  \>'2g]i  the  losses  incident  to  the  rapid 
motion  of  the  water  would  outweigh  the  gain.  Wheels  of  this 
kind,  however,  on  account  of  their  simplicity  have  found  appli- 
cation in  spite  of  their  inherent  lack  of  economy.  Among 
them  are  Whitelaw's  turbine  and  Barker's  mill. 

A  wheel  of  the  form  indicated  at  Fig.  133,  without  guides, 
would  operate  wholly  by  reaction.  The  water,  at  its  entrance 
to  the  wheel,  would  have  a  whirling  motion,  the  tangential 


CENTRIFUGAL  FORCE.  26$ 

component  of  which  is  equal  to  the  velocity  of  the  inner  cir- 
cumference. We  know  this  because  otherwise  the  water  could 
not  enter  the  wheel.  This  whirling  motion  is  not  the  direct 
effect  of  the  head,  but  is  imparted  to  the  water  mechanically 
by  the  action  of  the  wheel.  The  pressure  of  the  water  does 
not  diminish  till  the  latter  has  entered  the  buckets.  The 
energy  of  reaction  exerted  at  the  orifices  of  discharge  exceeds 
the  total  energy  due  the  head,  but  this,  as  we  have  already 
seen,  is  partly  absorbed  in  imparting  the  whirling  motion  to 
the  water  before  it  enters  the  wheel. 


CHAPTER    XIV. 
TURBINES. 

THE  Fourneyron  turbine  was  first  developed  in  France  in 
the  early  part  of  the  nineteenth  century.  M.  Fourneyron,  in 
1834,  received  the  prize  of  6000  francs  offered  by  the  Society 
for  the  Encouragement  of  the  Arts,  for  the  construction  of  the 
best  horizontal  *  wheel  on  a  large  scale.  This  was  the  first 
wheel  erected  by  M.  Fourneyron,  which  was  at  Pont  on  the 
river  Ognon.  This  circumstance  strongly  directed  the  atten- 
tion of  manufacturers  to  wheels  of  this  type,  and  before  1840 
many  such  wheels  of  imperfect  construction  and  small  size  had 
been  introduced  in  this  country.  These,  though  less  efficient 
than  the  ponderous  water-wheels  then  in  use,  won  their  way 
by  the  decided  advantages  they  offered  in  respect  of  compact- 
ness, rapidity  of  motion,  and  freedom  from  obstruction  by  back- 
water. 

About  1840,  Uriah  A.  Boyden  of  Massachusetts,  an  en- 
gineer of  rare  mechanical  ability,  applied  himself  to  the  study 
of  this  class  of  wheels.  The  time  being  ripe  for  discarding  the 
old-fashioned  breast-wheel,  he  had  a  very  successful  career  in 
designing  and  erecting  turbines  of  this  type,  in  which  he  made 
.•so  many  improvements  that  they  have  been  known  in  this 
country  as  Boyden  wheels.  Wheels  of  this  type  designed  by 
Mr.  Boyden  and  erected  in  the  mills  of  the  Appleton  Company 
at  Lowell,  in  1846,  were  found  upon  the  most  rigid  tests  to 

*  The  word  'horizontal'  is  used  ambiguously  in  reference  to  water- 
Avheels,  sometimes  denoting  a  wheel  revolving  in  a  horizontal  plane,  and 
sometimes  a  wheel  running  on  a  horizontal  shaft.  Here  it  has  the  former 
meaning. 

266 


THE  BO  YD  EN   TURBINE,  267 

yield  a  useful  effect  of  88  per  cent  of  the  absolute  power  of  the 
water,  a  result  which,  it  is  believed,  has  never  been  surpassed 
or  equalled  by  any  other  form  of  wheel,  though  higher  results 
are  often  claimed  by  inventors.  In  a  wheel  subsequently 
erected  for  the  Atlantic  Cotton  Mills  of  Lawrence,  where 
Mr.  Boyden  was  not  permitted  to  construct  a  weir  for  the 
measurement  of  the  discharge,  but  arrived  at  it  by  computa- 
tion, he  confidently  claimed  an  efficiency  of  92  per  cent. 

Mr.  James  B.  Francis,  engineer  of  the  Lowell  Water-power, 
designed  a  wheel  of  this  type  which  was  erected  in  the  Tremont 
Mills  of  Lowell.  In  1851  he  made  a  series  of  tests  and  meas- 
urements on  it  which,  from  their  completeness  and  the  care 
and  painstaking  accuracy  with  which  they  were  conducted, 
have  become  classic  in  engineering  literature.  These  are  fully 
reported  in  Mr.  Francis's  book,  "The  Lowell  Hydraulic  Ex- 
periments, ' '  *  comprising  ninety-two  experiments  made  under 
different  conditions  of  velocity  and  quantity  of  water.  These 
are  accompanied  by  complete  drawings  and  dimensions  of  the 
wheel,  which  make  these  results  invaluable  for  testing  theories 
of  the  action  of  water  in  the  turbine. 

This  wheel  is  shown  in  Fig.  135,  which  represents  it  in 
plan.  Fig.  136  is  a  vertical  section,  Fig.  136^  an  enlarged 
section  through  the  rim  of  the  wheel,  showing  the  disk  and 
gate.  W  is  the  wheel  proper,  consisting  of  an  upper  and  a 
lower  ring,  united  by  the  floats.  These  are  forty-four  in 
number,  of  Russia  iron  -fa  inch  thick,  inserted  in  grooves  cut  in 
the  rings.  Each  float  carries  several  tongues,  which  enter 
mortises  cut  through  the  rings  and  are  secured  by  cold  ham- 
mering. The  wheel  is  fastened  by  countersunk  screws  to  a 
broad  web  springing  from  the  hub,  which  is  secured  to  the 
shaft.  The  shaft  rises  through  the  penstock,  and  its  weight 
with  its  attachments  is  sustained  by  a  suspension-box  above 
the  crown  gear  which  delivers  the  power.  Surrounding  the 
shaft  is  the  disk-pipe  M  attached  to  the  penstock  at  the  top, 

*  Lowell  Hydraulic  Experiments.     Van  Nostrand  &  Co  ,  1868. 


268 


TURBINES. 


and  at  the  lower  part  to  a  broad  conoidal  plate  K  called  the 
disk,  to  which  are  attached  the  guides.  These  are  thirty-three 
in  number,  of  Russia  iron  ^  inch  thick,  curved  to  give  the 
proper  direction  in  entering  the  wheel,  attached  to  the  disk  by 
the  same  means  as  are  used  in  the  floats.  They  are  also  firmly 
united  to  the  lower  end  of  the  supply-pipe  or  penstock.  The 
regulating-gate  G  is  a  short  cylinder,  which  moves  telescope- 
wise  on  the  lower  part  of  the  penstock,  enters  the  annular  space 


FIG.  135. 

between  the  guides  and  floats,  and  closes  on  the  outer  edge  of 
the  disk,  thus  controlling  the  flow  of  water  to  the  wheel.  The 
guides  do  not  stand  perpendicular  to  the  disk,  but  are  inclined 
backward  in  a  direction  counter  to  that  of  the  wheel's  motion. 
This  wheel  did  not  give  so  high  a  result  as  the  wheels 
designed  by  Mr.  Boyden,  the  highest  efficiency  shown  being 
79  per  cent,  which  occurred  when  the  gate  was  fully  raised  and 
the  velocity  of  the  interior  circumference  of  the  wheel  was  62 
per  cent  of  that  due  the  head  acting  thereon,  although  the 


THE  BO  YD  EN    TURBINE. 


269 


270 


TURBINES. 


efficiency  stood  between  77  and  79,  while  the  relative  velocity 
varied  between  the  limits  of  47  and  70.  The  efficiency  of  this 
wheel  diminished  rapidly  as  the  discharge  was  reduced.  With 


R 

:     : 

- 

W 

,^—  v~-  '  —  '  —  ^  '  "    c      "  ~ 

;   ;      ;   \           --      ' 

FIG.  1360. 

Q  =  0.96  of  that  in  the  experiment  giving  the  best  result,  and 
the  relative  velocity  0.6 1,  the  efficiency  was 0.762 

For  Q  =  0.78,  relative  velocity  0.61,  efficiency  0.652 
0.525        "  "         0.56  "          0.44 

0.27          "  "         0.49          "         o.io 

0.26          "  "         0.27          "         0.24 

The  above  results  appear  to  show  that  the  speed  of  maxi- 
mum efficiency  diminishes  as  the  discharge  diminishes,  but  the 
wheel  is  usually  held  to  a  uniform  speed  whether  the  discharge 
be  small  or  great.  In  the  last  case  but  one  above,  had  the 
velocity  been  maintained  at  0.62,  the  efficiency  would  have 
been  still  less. 


DISCHARGE.  2/1 

A  Method  of  Computing  the  Discharge  of  Water  from  the 
Boyden  Wheel  at  Full  Gate. — We  will  use  the  following  nota- 
tion : 

Q  =  quantity  of  water  discharged  by  the  wheel ; 
h  =  head  of  water  acting  on  the  wheel ; 
F  =  cross-section  of  guide-passages  at  exit; 
Fl  =  cross-section  of  wheel-passages  at  entrance; 
F2  =  cross-section  of  wheel-passages  at  exit ; 
f  =  cross-section  of  wheel-passages  at  any  point  whose  radius 

is  r; 
c  =  velocity  of  discharge  from  F,  cl  do.  through  F^ ,  c2  do. 

from  F2; 

rl  =  radius  of  inner  ends  of  floats,  rz  do.  of  outer  ends ; 
oo  =  angular  velocity  of  wheel ; 
a  =  angle  between  tangent  of  guide  and  tangent  of  wheel  at 

extremity  of  former ; 

e  =  angle  between  direction  of  escaping  water  and  tangent  of 
wheel  at  extremity  of  float.  The  foot  and  second  are 
the  units. 

The  inner  ends  of  the  floats  make  substantially  a  right  angle 
with  the  circumference  of  the  wheel. 

Aside  from  the  centrifugal  force,  the  general  theory  of  the 
motion  of  water  in  the  wheel  may  be  stated  very  briefly.  We 
suppose  the  velocity  c  to  be  decomposed  into  its  radial  and 
tangential  components,  viz. ,  c  sin  a  and  c  cos  a. 

The  tangential  component  c  cos  a  is  inoperative  as  regards 
the  discharge.  It  simply  puts  the  water  in  a  position  to  enter 
the  wheel  without  any  effect  in  urging  it  through  the  wheel. 

At  the  entrance  to  the  wheel  there  is  a  loss  of  head,  being 
the  head  due  the  difference  between  ^  and  the  radial  com- 
ponent of  c,  viz. , 

— (c  sin  a  —  O2  =  — \c  sin  «  —  ^EN  =  — (sin  a  —  ~\  .  (41) 
2£-v  2g\  FJ       2g\  Fj 

There  is  a  loss  of  head  due  the  friction  of  the  water  in  the 
supply-pipe  and  the  guide-  and  bucket-passages,  which  might 


2;2  TURBINES. 

be  arrived  at  by  a  laborious  computation,  but  I  adopt  the  value 
given  by  Weisbach,*  viz.,  /,  f^  being  numerical  coefficients, 

c*  c2 

Frictional  head  =/— +/^. 

Weisbach  says,  "we  may  take/  =  /1  =  0.05  to  o.  10. "     I  put 

c* 
Frictional  head  =  0.15—, 

o 

which  is  about  the  mean  given  by  Weisbach.  I  also  adopt 
Weisbach's  coefficients  for  the  discharge  of  the  guide-  and 
bucket-orifices.  He  finds  that  the  cross-section  of  a  stream 
issuing  from  a  straight  pipe  is  about  3  per  cent  less  than  that 
of  the  pipe,  while  a  very  slight  convergence  diminishes  the 
cross-section  by  5  per  cent,  which  I  adopt. 

As  soon  as  the  water  takes  part  in  the  rotary  motion  of  the 
wheel,  it  is  acted  on  by  centrifugal  force.  Writers  on  the  tur- 
bine have  generally  estimated  this  force  upon  the  assumption 
that  the  water  has  the  same  angular  velocity  as  the  wheel,  and 
have  thus  arrived  at  a  very  simple  expression,  though  a 
decidedly  erroneous  one,  for,  while  the  bucket  may  be  moving 
to  the  right  with  the  angular  velocity  07,  a  particle  of  water  is 
moving  to  the  left  with  a  certain  angular  velocity  which  we  will 
call  ojp  which  is  very  small  at  the  entrance  to  the  wheel,  but 
becomes  considerable  toward  the  efflux.  The  true  angular 
velocity,  therefore,  is  GO  —  <ov  and  the  true  centrifugal  force 
acting  on  a  mass  Mis  M(&>  —  aa^r. 

We  must  next  determine  the  head  due  the  centrifugal  force, 
by  finding  the  work  done  by  the  same  on  a  given  weight  of 
water  while  passing  through  the  wheel,  and  dividing  the 
result  by  the  weight.  To  attempt  this  by  the  strict  methods 
of  the  calculus  would  lead  to  a  hopelessly  complex  expression. 
As  in  many  hydraulic  problems  we  shall  find  an  advantage  in 
approximating  the  truth  by  a  rough  graphical  process  of  inte- 
gration. At  a  point  whose  distance  from  the  centre  is  r,  let 
d  represent  the  angle  between  the  tangent  of  the  float  and 

*  Hydraulics.     Du  Bois's  translation,  p.  359. 


DISCHARGE. 


273 


radius  of  the  wheel,  /being  the  section  of  the  bucket  (space 
between  two  consecutive  floats),  by  a  cylindrical  surface  con- 


centric   with   the   wheel 

expression  for  centrifugal  force  becomes 


Then  GO^  —  c  —    tan   d,    and    the 


(42) 


--        tan2  d).   . 


Dividing  the  bucket  into  any  number  of  parts  by  concentric 
cylindrical  surfaces,  we  can  compute  the  coefficients  of  of*,  GOC, 
and  c2  for  each  part.  From  the  full-size  drawings  of  the  wheel, 
and  from  the  data  given  by  Mr.  Francis  in  the  Lowell 
Hydraulic  Experiments,  I  obtain  the  following  values:  rl  = 
3.375  feet,  r2  =  4.146  feet,  F  —  6.53  square  feet,  F^  =  19.35 
square  feet,  F2  =  7.467  square  feet,  a  =  19°  5'.  From  these, 
together  with  the  several  values  of  d  and  /  I  construct  the 
following  table.* 

TABLE   2. 


Radius 
r. 
Inches. 

Distance  from  Inner  Edge 
of  Crown,  measured  on 
Radius  of  Wheel. 
Inches. 

f.  Area  of  Float-  passage 
or  Bucket  measured  on 
Cylindrical  Surface  of 
Radius  rl  concentric 
with  Wheel.  Sq.  Ft. 

d  =  Angle  between  Tan- 
gent of  Float  and  Ra- 
dius of  Wheel. 

p 
—  ?tan  d  =  Numerical  Co- 
44.X 
efficient  of  c  in  the  Ex- 
pression for  the  Relative 
Tangential  Velocity. 

Numerical  Coefficient  in  the 
Expression  for  the  Centrifugal 
Force  of 

., 

lac 

- 

41 

42 
43 
44 
45 
46 
47 
48 
49 
49.625 

49-75 
Sum  o 
^ofd 

0-5 
1-5 
2-5 
3-5 
4-5 
5-5 
6-5 
7-5 
8-5 
9-125 

9.25 
f  the  first 

Q 

0-4397 
0.4418 
0.4430 
0.4460 
0.4506 
0.4564 
0.4639 

0-4739 
0.4868 
0.5064 

9  coefficier 

4°   27' 
13     43 

23      20 

32     47 
39     55 
48     37 
54    4i 
62     06 
69     38 
77     18 
Ext'mitv 
78°  27' 
ts  and  i  c 

0.0263 
O.082O 
0.1445 
0.2143 
0.2756 
0.3691 
0.4515 
0.5915 
0.8232 
1.3006 

f  the  roth 

3-417 

3-500 
3-583 
3.667 
3-750 
3-833 
3-917 
4.000 
4-083 
4-135 

0.0526 

o.  1640 

0.2890 
0.4286 
0.55^2 

0.7382 

o  .  9030 

I.083O 
1.6464 
2.6012 

0.0002 

o.ooig 
0.0058 
0.0125 

O.O202 

0.0355 
0.0520 
0.0875 
0.1660 
0.4091 

2.899 

6.5063 
0.5422 

0.4839 
0.0403 

*  This  mode  of  determining  the  discharge  of  the  turbine  was  published 
in  the  Journal  of  the  Franklin  Institute  for  July,  1884. 


274  TURBINES. 

The  centrifugal  force  is  represented  by  the  expression 

(M=  -^34.784^  -  6.50630*  -f-  0.4839^),    .     (43) 

in  which  M  is  the  mass  and  Wihe  weight  of  water  included 
between  two  consecutive  sections  one  inch  apart;  one-fourth 
the  value  of  the  last  coefficient  being  taken  because  this  applies 
only  to  J  inch.  The  expression  may  also  be  understood  to 
represent,  in  inch-pounds,  the  work  done  by  centrifugal  force 
on  the  said  mass  while;  passing  through  the  wheel  ;  hence  the 
division  by  12  to  reduce  it  to  foot-pounds.  The  head  due  the 
centrifugal  force  is  represented  by 

5.7980/5  —  1.08440*:  +  0.0806^ 

-^-  -'       '     '     (44) 

This  expression  in  the  formula  for  discharge  takes  the  place  of 


2g 

given  generally  by  writers  on  the  turbine. 

The  principles  stated  in  what  'precedes  may  be  expressed 
algebraically  as  follows  : 

c?  <*  c*  I. 

-*-  =  A  --  cos2  a—  —Ism  a—  «• 

2f  zg  2f\  F 

-  ^^  +  ^(5-798^-1.08440^  +  0.0806^).     (45) 

Or,  substituting  numerical  values,  reducing,  and  observing  that 

F 
C2  =  c~p^  we  Set 

^2 

1.7277^  =  2gh  +  5.798032  _  1.0440*,    .      .     (46) 

and  Q  =  o.g^Fc. 

The  results  given  in  Table  3  are  computed  by  this  formula. 
They  are  arranged  according  to  the  ascending  values  of  a?,  and 
embrace  in  reality  the  entire  series  with  full  gate,  the  experi- 


DISCHARGE. 


275 


ments  omitted  being  substantially  nothing  more  than  repetitions 
of  those  included. 

TABLE  3. 


Q 

Number  of 

• 

10   =  2JT«. 

h 

Discharge  in  Cubic  Feet  per 

the  Experi- 
ment in 

Number  of 

Angular 

Head  Acting 
on  the  Wheel 

Second. 

Mr.  Fran- 
cis's Series. 

the  Wheel  per 
Second. 

the  Wheel. 
Feet  per  Sec. 

Feet. 

By  Experiment 

By  Computa- 
tion. 

43 

0 

O 

12.797 

135-65 

135.41 

42 

0.45431 

2.8534 

12.948 

133-43 

134-57 

41 

0.53232 

3-3447 

12.977 

133-75 

135.19 

40 

o.  60000 

3.7699 

12.973 

134-80 

I35.76 

39 

0.64702 

4-0653 

12.963 

135-34 

136.20 

36 

0.69471 

4.3650 

12.944 

136.49 

136.69 

35 

0.74211 

4.6628 

12.939 

137-71 

137-31 

34 

0.78401 

4.9261 

12.941 

138-09 

137.98 

32 

0.83624 

5-2542 

12.915 

138.27 

138.68 

29 

0.86643 

5-4439 

12.906 

138.51 

139-18 

21 

0.90201 

5-6675 

12.899 

139.90 

I39-80 

18 

0.94507 

5-938o 

I2.88O 

140.47 

140-56 

16 

0.99945 

6.2797 

12.890 

141.98 

141.76 

15 

.02373 

6.4323 

12.888 

142.04 

142.28 

14 

.06744 

6  .  7069 

12.856 

142.52 

I43-I5 

ii 

.12518 

7.0697 

12.819 

I43-9I 

144.38 

10 

.18460 

7-4431 

12.800 

144-87 

I45-83 

9 

•24514 

7-8234 

12.777 

146.02 

I47-38 

8 

•  30933 

8.2268 

12.720 

147.29 

148.98 

7 

.38249 

8.6864 

12.696 

149.47 

151.08 

6 

.46149 

9.1828 

12.653 

152.27 

153-41 

5 

.53218 

9.6270 

12.611 

154-39 

155-57 

4 

-59651 

10.0313 

12.554 

156.65 

157-57 

13 

.  78404 

11.2095 

12.510 

163.43 

164.26 

The  reduced  efficiency  at  part  gate,  or,  in  other  words,  the 
inability  to  use  a  small  quantity  of  water  with  the  same  effi- 
ciency as  a  large  one,  is  an  inherent  defect  of  the  turbine  and 
is  very  strikingly  apparent  in  the  one  under  consideration,  the 
useful  effect  being  not  more  than  40  per  cent  when  the  dis- 
charge is  reduced  one-half,  and  so  small  with  a  discharge  of 
one-fourth  that  it  is  hardly  worth  while  to  raise  the  gate.  To 
realize  the  cause  of  this  difficulty  we  must  consider  how  the 
water  traverses  the  guides.  When  the  gate  is  fully  raised,  R, 
Fig.  1 360,  the  water  which  enters  at  the  top  of  the  wheel  fol- 
lows the  curve  of  the  garniture  Z.,  and  takes  the  direction  of  the 
extremity  of  the  guide  at  its  entrance  to  the  wheel ;  but  when 


2/6  TURBINES. 

the  gate  is  partly  closed,  as  indicated  by  the  dotted  lines,  a 
part  of  the  water  follows  the  inner  surface  of  the  gate,  and 
reaches  the  opening  in  a  vertical  direction  with  no  tangential 
velocity ;  tending  to  enter  the  wheel  in  a  radial  direction  as  if 
escaping  from  an  orifice  in  a  direction  perpendicular  to  the 
plane  thereof.  The  more  the  gate  is  closed  down,  the  more 
the  opening  loses  the  character  of  a  channel  and  acquires  the 
character  of  an  orifice,  and  the  more  the  direction  of  the  escap- 
ing water  departs  from  that  of  the  tangent  and  approaches 
that  of  the  radius.  The  closing  of  the  gate  alters  the  direction 
of  the  water  entering  the  wheel  and  impairs  the  efficiency 
with  which  it  acts  thereon.  This,  however,  is  not  the  only  ill 
effect,  and  probably  not  the  worst.  The  stream  entering  the 
bucket  does  not  fill  and  pass  smoothly  through  the  same  as  it 
does  at  full  gate,  but,  a  part  of  the  bucket  being  necessarily 
filled  with  dead  water,  the  stream  wastes  its  energy  in  commo- 
tion and  eddies  while  traversing  the  wheel. 

A  great  many  devices  have  been  introduced  to  obviate  this 
difficulty,  and  it  is  to  this  object  that  the  efforts  of  inventors 
have  been  mainly  directed.  A  considerable  measure  of  success 
has  attended  these  efforts,  but  it  has  been  attained  at  the  sacri- 
fice of  some  percentage  of  efficiency  at  full  gate.  Mr.  Boyden's 
expedient  for  meeting  the  difficulty  was  by  giving  an  inclined 
direction  to  the  guides.  The  outer  extremity  of  the  guide  was 
inclined  in  a  direction  reverse  to  that  of  the  wheel's  motion, 
making  an  angle  of  60°  or  less  with  the  horizontal.  The  water 
which  passed  down  along  the  inside  of  the  cylindrical  gate 
pursued  a  spiral  pathway  and  reached  the  opening  with  a  con- 
siderable tangential  element  of  velocity.  The  guides  in  the 
Tremont  turbine  had,  as  appears  from  the  cuts,  a  slight  inclina- 
tion of  this  kind,  but  not  enough  to  affect  the  efficiency.  To 
realize  the  full  benefit  of  this  disposition  the  guides  would 
require  an  inclination  of  less  than  30°  to  the  horizontal,  an 
arrangement  involving  grave  structural  difficulties.  I  know  of 
no  experiments  to  show  how  much  this  disposition  increased 
the  efficiency. 


EFFICIENCY  AT  PART  GATE.  277 

Another  expedient  is  by  attaching  to  the  gate  a  curved 
block  or  shell,  Fig.  136^,  in  the  form  of  the  garniture  or 
curb  L.  This  contracts  the  channel  of  the  guide  as  the  gate 
descends,  and  thus  forces  the  water  to  follow  the  direction  of 
the  guides. 

The  most  promising  method  of  meeting  the  difficulty  inci- 
dent to  the  passage  of  the  water  through  the  wheels  is  by 
dividing  the  float-passages  into  several  parts  by  horizontal 
diaphragms.  This  device  was  adopted  in  the  earliest  form  of 
the  Fourneyron  turbine,  and  was  used  in  many  cheaper  forms 
of  wheel  in  this  country,  made  wholly  of  cast  iron.  Its  intro- 
duction in  the  higher  grade  of  wheels  with  sheet-iron  floats 
involved  constructive  difficulties.  It  has  been  recently  adopted 
in  the  wheels  of  the  Niagara  Falls  Power  Company  at  Niagara 
Falls.  The  only  perfect  method  of  obviating  the  loss  incident 
to  part  gate  would  consist  in  a  device  to  contract  simultaneously 
both  the  guide-  and  the  float-passages  according  to  the  re- 
quirements of  the  power. 

The  improvements  in  the  turbine  which  have  been  effected 
since  Mr.  Boyden's  time  are,  in  addition  to  an  increased 
efficiency  at  part  gate,  a  great  diminution  of  the  cost,  the 
development  of  the  draft-tube,  and  the  adaptation  of  the  wheel 
to  a  horizontal  shaft.  As  to  the  wheel  itself,  meaning  the 
revolving  part  carrying  the  organs  on  which  the  water  acts,  it 
has  almost  universally  taken  the  form  of  Fig.  137,  in  which  the 
water  enters  the  wheel  through  openings  having  their  longest 
dimensions  parallel  to  the  shaft,  and  leaves  it  through  openings 
which  have  their  longest  dimensions  radial.  The  differences 
between  the  wheels  of  different  makers  consist  in  the  guides, 
gates,  and  mode  of  regulating  the  supply  of  water.  It  will  be 
readily  perceived  that  the  form  of  float,  Fig.  137,  is  not  con- 
sistent with  the  highest  efficiency,  the  imperative  condition  of 
which  is  that  the  water  should  escape  from  the  float-passages 
with  a  velocity  equal  to  that  of  the  float  and  in  a  direction  con- 
trary to  that  of  the  float's  motion,  a  condition  which  cannot  be 
realized  in  this  form  of  wheel.  Except  in  so  far  as  the  motion 


278  TURBINES. 

of  the  water  is  affected  by  centrifugal  force,  it  has  the  same 
velocity  at  the  inner  end  of  the  opening  as  at  the  outer  end, 
while  the  velocity  of  the  float  at  the  latter  point  may  be  more 
than  twice  as  great  as  at  the  former. 


FIG.  137. 

•  The  Swain  Wheel,  shown  in  Figs.  138,  1380,  and 
is  one  of  'die  most  successful  of  existing  types,  especially  as 
regards  the  difficulties  incident  to  part  gate.  Fig.  138  is  a 
vertical  section  through  the  centre  of  the  wheel,  Fig.  138^  a 
plan  of  a  portion  of  the  wheel  and  gate,  Fig.  138^  a  develop- 
ment of  the  outer  surface  of  the  wheel. 

I  describe  it  in  the  language  of  Mr.  James  B.  Francis  con- 
tained in  his  report  of  a  test  of  a  72-inch  wheel  of  this  con- 
struction at  the  Booth  Cotton  Mills,*  Lowell,  in  1874. 

The  lower  curb,  C,  is  a  strong  disk  of  cast  iron,  with  a  short 
cylinder  upon  which  the  gate  moves,  and  an  inner  tube  with 

•Journal  of  the  Franklin  Institute,  April,  1875. 


THE   SWAIN    WHEEL. 


2/9 


diverging  sides,  through  which  the  water  leaving  the  wheel  is 
discharged  into  the  pit.      There  are  three  arms  reaching  from 


FIG. 


FIG.  138-5. 


the  sides  of  this  tube  to  the  hub,  which  forms  the  pintle  upon 
which  the  wheel  revolves.  The  step  S  is  a  cylinder  of  white 
oak,  with  conical  ends,  and  is  free  to  revolve  with  the  wheel 


280  TURBINES. 

or  to  remain  stationary  upon  the  pintle  while  the  wheel  revolves 
around  it.  By  means  of  pipe  (/")  water  is  supplied  to  the  step, 
passing  through  its  centre  and  escaping  outward  over  its  ends. 
The  intermediate  aa  connecting  the  shaft  c  and  the  wheel- 
coupling  v  can  be  removed  to  replace  the  step  without  disturb- 
ing either  the  wheel  or  the  shaft.  The  screws  tt'm  the  flange 
of  the  shaft  are  used  to  adjust  the  wheel  vertically. 

The  gate  G  was  made  with  two  cylinders,  N  and  M, 
attached  at  their  tops  to  a  disk  Q,  which  forms  an  angle  of  80° 
with  the  cylinders.  At  the  lower  end  of  the  outer  cylinder  is 
a  narrow  flange  to  which  is  fastened  the  leather  packing,  which 
prevents  the  escape  of  water  between  the  gate  and  the  lower 
curb.  The  gate  has  twenty-four  guides,  three  of  them  being 
of  cast  iron  and  of  the  form  shown  in  the  plan  at  e.  The 
other  guides,  twenty-one  in  number,  are  of  bronze,  0.23  inch 
in  thickness  and  18.94  inches  long.  These  are  sharpened  at 
each  end  to  0.04  inch  in  thickness,  with  a  bevel  on  each  side 
one  inch  long;  and  are  so  set  as  to  form  an  angle  of  14°  with 
the  tangent  to  the  wheel  passing  through  their  inner  edges. 

Outside  of,  and  in  a  line  with,  the  thick  guides  are  placed 
three  stands,  one  of  which  is  seen  at  O,  Fig.  138.  These 
support  the  chamber  E  and  the  wheel-cover  L.  The  lower 
disk  of  this  chamber  is  slotted,  so  that  the  guides  may  enter 
the  chamber  when  the  gate  is  raised,  by  means  of  the  hoisting- 
rods  which  pass  through  the  thick  guides.  The  gate  is  shown 
as  fully  opened.  The  gate  is  opened  by  lowering,  and  closed 
by  raising  it,  so  that  when  the  gate  is  first  opened,  the  water 
is  admitted  into  the  wheel,  immediately  under  the  crown,  and 
the  depth  of  the  section  of  the  stream  passing  through  the 
guides  is  increased  in  proportion  as  the  gate  is  opened.  The 
lower  edge  of  the  chamber  and  the  upper  edge  of  the  gate  are 
finished  so  as  to  form  a  close  joint  when  brought  into  contact. 
The  inner  edges  of  the  guides  are  if  inches  distant,  radially, 
from  the  outer  edges  of  the  buckets. 

The  wheel  Wis  72  inches  in  diameter  at  the  outer  edges 
of  the  buckets,  and  23.35  inches  in  depth  from  the  under  side 


THE   SIVA  IN    WHEEL.  28 1 

of  the  crown  to  the  lower  edges  of  the  band.  It  has  twenty- 
five  buckets  of  bronze,  these  being  formed  between  dies  in  a 
press  and  having  the  crown-plate  and  the  lower  band  cast  upon 
them  of  iron. 

Fig.  1 3$a  is  a  horizontal  section  just  below  the  crown-plate, 
and  represents  the  form  of  the  bucket  for  the  first  six  inches 
below  the  crown. 

Fig.  138^  is  a  development  of  a  portion  of  the  cylindrical 
surface  of  the  wheel  containing  the  outer  edges  of  the  buckets. 
The  discharging  edge  of  the  bucket  lies  in  a  vertical  plane 
passing  through  the  axis  of  the  wheel,  and  is  parallel  to  this 
axis,  from  the  under  side  of  the  crown,  to  a  point  about  8£ 
inches  below  it,  and  from  this  point  is  continued  in  the  form  of 
a  quadrant  having  a  radius  equal  to  one-fifth  of  the  diameter  of 
the  wheel,  and  having  its  centre  in  the  cylinder  forming  the 
outer  circumference  of  the  wheel ;  thus  forming,  in  connection 
with  the  surface  of  the  adjoining  bucket,  an  outlet  which  is  in 
effect  a  union  of  two  wheels,  an  inward  discharge  and  a  down- 
ward discharge. 

The  following  measurements  were  made  at  the  mill  before 
the  wheel  was  started : 

Vertical  distance  from  under  side  of  crown  to  the 

lower  edge  of  the  buckets 23-35  inches. 

Vertical   distance    from  the   under    side    of  the 

crown  to  the  top  of  band  B 13.285      " 

Total  area  of  outlets   of  wheel  (twenty-five  in 

number) 9.558  sq.  ft. 

Vertical  movement  of  speed-gate 13.08  inches. 

Mean  shortest  distance  from  the  inner  edge  of 
one  guide  to  side  of  adjacent  guide  (twenty- 
four  in  number) 4. 5  32  n ' 

Total  area  of  inlet  in  speed-gate 9.880  sq.  ft. 

It  will  be  perceived  that  centrifugal  force,  in  this  wheel, 
operates  to  diminish  the  discharge  instead  of  to  increase  it  as 
in  the  case  of  the  Boyden  wheel.  The  importance  of  this 


282 


TURBINES. 


TABLE   4.— TESTS   OF   DISCHARGE   AND    EFFICIENCY   OF    THE 
SWAIN    TURBINE. 


72-iNCH  WHEEL  AT  BOOTH  COTTON-MILLS, 
LOWELL,  AUGUST,  .874. 

36-INCH  WHEEL  AT  HOLYOKE  TESTING-FLUME, 
JANUARY,  1897. 

^ 

J!2-d 

0 

= 

I 

«2,j 

B 

£ 

Number  of  Experiment. 

Height  of  Speed-gate. 

Head  Acting  on  the  Wheel 

Discharge  in  Cubic  Feet  p 
Second. 

Ratio  of  the  Velocity  of  i 
Exterior  Circumference 
the  Velocity  due  the  Hei 

Ratio  of  the  Useful  Effect 
the  Power  Expended. 

Number  of  the  Experiment 

Height  of  Speed-gate,  F 
Height  being  i.ooo. 

Head  Acting  on  the  Wheel 

£ 

u 

c 

11 

Q 

Ratio  of  the  Velocity  of  ' 
Exterior  Circumference 
the  Velocity  due  the  He 

Ratio  of  the  Useful  Effect 
the  Power  Expended. 

Percentage  of  Full  Discha 

In        Feet. 

In. 

Feet. 

3.25 

3-96       70.86 

0.706 

°-595 

i 

0.067 

16.49 

12.80 

0.739 

o..6, 

4 
5 

•°3 

72.49 

0-523 

0.580 

3 

16.18 

19.24 

0-377 

0.245 

6 

93 

69.54 

0.772 

0-589 

6 

.6.,  7 

19.62 

0.653 

0.43° 

0.249 

7 

6.5o 

.36 

108.  ii 

0.852 

0-715 

7 

16.07 

19.76 

0.6.9 

0.449 

0.252 

8 

.28 

iit-55 

0.779 

0.757 

8 

16.01 

.9.89 

0.582 

0.460 

0.254 

JO 

.27 

"3-45 

0.734 

0.774 

9 

16.03 

20.06 

0.545 

0.464 

0.257 

14 

•  32 

.16.13 

0.677 

0.779 

10 

0.250 

15-79 

27.64 

0.885 

0.440 

.356 

15 

•25 

116.60 

0-555 

0.721 

12 

15-70 

rr     £1 

29.26 

0.808 

0.572 

-378 

26 

.28 

49-21 

0.792 

o^io 

16 

I5.OI 

3°  -5? 
3'  -46 

0.661 

0.659 

.407 

31 

.19 

51.67 

0.510 

0.463 

Z7 

!5-57 

3'.83 

0.628 

0.642 

.412 

32 

3.00 

.98 

68.75 

0.512 

0.541 

18 

15-54 

32.1. 

0.596  ' 

0-645 

.416 

40 

.05 

63.10 

0.003 

0.453 

19 

15-53 

32.40 

0.564 

0.640 

.420 

41 

4.00 

.90 

72.76 

0.967 

0.423 

27 

0-375 

15-30 

38.57 

0.837 

0.682 

.504 

45 

•76 

81.49 

0.766 

0.646 

21 

15.21 

40.01 

0.765 

0.724 

•524 

49 

•  70 

83.89 

0.648 

0.666 

24 

.5.21     41.58 

0.670 

0.746 

•545 

50 

5.00 

•44 

96.86 

0.695 

0.717 

25 

15.19    42.06 

0.64. 

0.748 

•552 

53 

•44 

97.82 

0.517 

0.657 

26 

15.21!   42.50 

0.604 

0.738 

•557 

57 

•55 

94.86 

0.76. 

0.706 

•2'., 

0.500 

15-96 

49-62 

0.801 

0-773 

-635 

60 

.66 

86.85 

0.931 

0.551 

30 

15.91 

50.87 

0738 

0.795 

.652 

69 

6.00 

.28 

110.09 

0.669 

0.761 

33 

15.78 

52-54 

0.647 

0.805 

.676 

72 

7.00 

•  3Q 

103-59 

0.981 

0.543 

34 

I5-74 

52.58 

0.608 

0.791 

.683 

75 

.16 

116.71 

0.766 

35 

0.625 

15-65 

55  -32 

0.839 

0.776 

80 

.09 

121.56 

o'.657 

0.787 

39 

I5.43 

58.95 

0.709 

0.845 

'767 

90 

8.00        97 

130.25 

0.698 

0.806 

4° 

15-38 

•775 

103 

9.00       .84 

.38.84 

0.710 

0.829 

42 

0.750 

15.20 

62  o£ 

0.818 

O.83T 

.8.4 

108 

10.00       .91 

128.57 

0.969 

0.620 

44 

15.62 

64.09 

0.780 

0.850 

.829 

in 

•74 

.43.26 

0.762 

0.831 

45 

15-54 

64.64 

0-744 

0.854 

.838 

1*3 

.68 

M4-77 

0.708 

0.836 

46 

15-70 

65.4. 

844 

122 

12.00 

•77 

143-44 

0.950 

0.690 

53 

0.875 

.5.28 

70.01 

0.705 

0.845 

9.6 

"3 

•52 

.56.70 

0-749 

0.838 

54 

IS-IJ 

70.42 

0.683 

0.845 

.925 

I27 

•49 

158.46 

0.600 

0-775 

56 

I.OOO 

15-33 

70.58 

0.807 

0.798 

.922 

128 
129 

13.08 

Full 

.10 

.88 

.20.39 
137-87 

1.174 

0.206 
0.499 

8 

15-44 

15-47 

72.73 

0^767 

0.809 
0.821 

934 
945 

130 

Ht. 

.603 

149-13 

0^968 

0.690 

59 

15-48 

73-45 

0.750 

0.830 

954 

131 

.480 

158.88 

0.866 

0.803 

60 

15-43 

74.19 

0.730 

0.836 

966 

T33 

•37 

162.54 

0.770 

0.836 

61 

74-74 

0.843 

973 

'36     , 

•37 

164.24 

0.727 

0.830 

62 

15-4° 

75-52 

0.700 

0.846 

984 

142 
M3 

.40 
2.40 

165.03 
162.85 

0.746 
0.627 

63 
64 

£3 

75-98 
76.49 

^656 

0.848 
0.848 

995 
004 

144 

3-17 

117.84 

1.193 

0.000 

action  is  apparent  when  we  compare  expt.  143  with  144,  which 
were  both  made  with  the  same  height  of  gate.  Had  the  head 
been  1 3  feet  in  each  of  these  cases,  other  conditions  remaining 


THE   SWAIN    WHEEL.  283 

the  same,  the  discharge  would  have  been  166.75  cubic  feet  per 
second  in  143,  and  117.06  in  144.  This  difference  of  49.69 
cubic  feet  per  second  is  due  to  an  increase  in  the  angular 
velocity  oo  from  4.12  in  143  to  11.56  in  144.  We  have 
already  adverted  to  the  apparently  unscientific  character  of  a 
wheel  with  radial  orifices,  page  259.  The  vertical  edge  of  the 
float,  in  this  wheel,  moves  with  a  velocity  less  than  three- 
fourths  that  of  the  horizontal  edge  near  its  extremity,  and  both 
velocities  could  not  bear  the  right  proportion  to  the  velocity  of 
the  water  if  the  latter  was  uniform.  We  see  how  the  centrif- 
ugal force  goes  far  toward  obviating  the  ill  effect  of  this  dis- 
position. The  water  at  the  outer  part  of  the  orifice  is  actually 
discharged  under  a  greater  head  than  at  the  inner  part,  and  so 
conforms  more  nearly  to  the  theoretical  conditions  of  efficiency 
than  would  appear  without  considering  the  action  of  centrifugal 
force.  Nevertheless  it  may  be  safely  affirmed  that  the  highest 
efficiency  can  never  be  obtained  from  a  wheel  with  radial 
orifices,  or  orifices  lying  in  a  plane  perpendicular  to  the  shaft. 
The  highest  efficiency  yet  obtained  for  the  Swain  wheel  is 
85.4,  while  the  Boyden  wheel,  as  stated,  showed  88.  This 
difference  must  be  attributed  to  the  difference  in  the  character 
of  the  orifices  of  discharge. 

The  maximum  efficiency  in  the  trials  of  1874  was  83.6  in 
expt.  1 13,  with  a  relative  velocity  of  6.708,  and  a  discharge  of 
144.77,  the  gate  not  being  fully  raised.  Substantially  the  same 
efficiency  was  found  in  expt.  133,  with  the  gate  fully  raised,  ai 
discharge  of  162.54,  and  a  relative  velocity  of  0.77,  though  the' 
efficiency  did  not  fall  below  82,  while  the  relative  velocity  varied 
from  0.71  to  0.81.  As  the  head  varied  considerably  during 
the  trials,  it  is  better,  for  purposes  of  comparison,  to  reduce  the 
discharge  to  a  uniform  head.  This  was  done  by  Mr.  Francis 
in  his  report  of  the  trials,  in  which  he  gave  the  discharge  corre- 
sponding to  a  uniform  head  of  17  feet.  This  calculation  is 
made  upon  the  principle  that  the  discharge  is  as  the  square  root 
of  the  head.  That  is  to  say:  If  for  a  head  of  12.372  feet  the 
discharge  is  162.54,  then  for  a  head  of  17  feet  the  discharge 


284  TURBINES. 


will  be   162.54*7 '- —  =  190.53.      Three-fourths  of  this  is 

142.90.     With    this   discharge  and  nearly  the  same   relative 
velocity  the  efficiency  was  about  80. 

With  one-half  of  full  discharge,  viz.,  near  95  cubic  feet  per 
second,  on  17  feet  head  and  a  relative  velocity  of  0.65  to  0.75, 
the  efficiency  was  65  to  67.  With  about  one-fourth  the  full 
discharge  and  the  same  relative  velocity  we  get  an  efficiency 
of  something  over  40.  So  far  as  this  series  of  trials  goes, 
therefore,  we  are  entitled  to  say  that  the  wheel  gives  an  effi- 
ciency of  near  84  at  full  discharge,  So  at  three-fourths,  65  at 
one-half,  and  about  40  at  one-fourth. 

The  tests  of  January,  1897,  show  some  improvement  in  the 
wheel,  as  compared  with  those  of  1874,  the  best  efficiency  in 
this  series  being  a  little  over  85,  which  occurs  with  about  five- 
sixths  of  the  full  discharge,  and  a  velocity  about  three-fourths 
that  due  the  head.  It  would  appear  from  the  table,  however, 
that  the  proper  velocity  for  the  wheel  would  be  about  two-thirds 
that  due  the  head.  With  this  velocity  the  efficiency  is  sub- 
stantially 85  at  full  discharge,  75  at  one-half  discharge,  and 
43  at  one-fourth. 

Fig.  139  is  a  section  of  the  vertical  Swain  wheel  in  its 
present  form.  The  only,  essential  change  consists  in  dispens- 
ing with  the  chamber  into  which  the  guides  rise  when  the  gate 
is  closing.  The  guides  are  not  attached  to  the  gate  but  to  the 
fixed  curbs  of  the  wheel,  and  pass  through  slots  in  the  horizon- 
tal rim  of  the  gate,  which  closes  by  rising  as  before.  G  is  the 
gate,  /  the  float,  g  the  guide.  In  the  former  arrangement, 
where  the  guides  were  cast  in  one  piece  with  the  gate,  they 
frequently  broke  at  their  junction  with  the  latter  in  consequence 
of  the  vibrations.  This  accident  does  not  occur  in  the  present 
arrangement.  Properly  the  edges  of  the  floats  should  appear 
in  elevation  in  the  figure,  but  this  feature  is  omitted.  No  im- 
provement has  been  made  in  the  step-bearing,  which  consists 
of  a  conical  block  of  wood,  thoroughly  dried  and  soaked  in  hot 
tallow.  A  hole  is  bored  through  the  centre  of  the  step  through 


THE   SWAIN    WHEEL. 


285 


which  water  brought  by  the  pipe'/"  passes  and  spreads  over  the 
conical  surface.  An  '  improvement  of  some  value  has  been 
made  in  the  means  of  replacing  the  step.  To  do  this  the 
spool-shaped  piece  T  is  removed  by  taking  out  the  screws. 


FIG.  139. 

The  wooden  bearing-piece  P,  resting  on  the  iron  cap,  is  taken 
out  with  the  latter,  the  step  is  removed  and  a  new  one  dropped 
in  its  place. 

Fig.  140  shows  a  pair  of  Swain  wheels  on  a  horizontal  shaft. 

'This  shaft  passes  through  stuffing-boxes,  and  at  the  left  end 

has  a  thrust-bearing,  to  meet  the  considerable  thrust  that  exists 

when  one  wheel  is  out  of  use.      At  the  opposite  end  the  shaft 

runs  in  a  stuffing-box  bearing.      The  guide,   gate,  and  floats 


286 


TURBINES. 


THE  AMERICAN    TURBINE.  287 

are  indicated  by  the  same  letters  as  before.  This  arrangement 
is  admirably  adapted  to  a  wide  variation  in  the  consumption  of 
water.  With  both  wheels  running  at  full  gate,  the  water  is 
used  with  high  efficiency,  and  the  consumption  is  at  its  maxi- 
mum. When  the  consumption  falls  to  half  the  maximum,  the 
water  begins  to  be  used  with  poor  efficiency.  One  gate  is  then 
closed,  and  the  other,  under  the  action  of  the  regulator,  opens 
to  full  width,  and  the  water  continues  to  act  with  high  efficiency 
till  the  consumption  is  reduced  to  about  half  the  capacity  of 
one  Avheel,  or  about  one-fourth  the  maximum  discharge.  To 
avoid  running  the  unused  wheel  in  the  water,  the  dividing  par- 
tition between  the  two  w"heels  is  continued  to  low  water,  form- 
ing a  separate  draft-tube  for  each  wheel.  A  small  valve,  not 
shown,  is  opened  in  the  draft-tube  pertaining  to  the  unused 
wheel,  admitting  air  and  causing  the  water  to  disappear. 

The  American  Turbine. — The  Western  States  of  the  Union 
had  use  for  water-power  from  their  earliest  settlement.  Com- 
munication with  the  older  parts  of  the  country,  at  that  time, 
was  slowr  and  expensive.  For  such  heavy  articles  as  water- 
wheels  the  cost  of  transportation  was  prohibitive,  and  the 
people  were  obliged  to  adopt  such  makeshifts  as  they  could 
devise.  Among  the  early  ^settlers  were  many  skilful  mechanics, 
and  necessity,  the  mother  of  invention,  led  to  the  development 
of  turbines  without  much  regard  to  the  traditions  of  the  en- 
gineering profession,  the  learning  of  the  schools,  or  the  laws 
of  hydraulics ;  though,  by  a  purely  experimental  process,  they 
have,  in  some  cases,  been  brought  more  or  less  into  conformity 
with  those  laws.  Of  course  many  wheels  of  very  crude  design 
have  been  put  on  the  market  in  that  region,  and  have  speedily 
disappeared,  but  certain  types  have  persisted  and  not  only  held 
the  market  in  that  section,  but  have  found  extended  application 
in  the  older  parts  of  the  country.  Among  these  is  the  wheel 
we  -are  now  considering.  In  this  case  the  revolving  wheel  is 
not  essentially  different  in  principle  from  the  Swain  wheel 
already  described,  though  it  differs  in  constructive  details, 


288 


TURBINES. 


being  cast  all  in  one  piece,  while  in  the  Swain  and  Boyden 
wheels  the  floats  are  separate  sheets  of  iron  or  steel,  attached 
to  the  crowns  and  rims  by  mechanical  means  or  set  up  in  the 
moulds  and  incorporated  with  the  wheel  in  casting. 

Fig.  137  shows  the  wheel,  i.e.,  the  running  part  removed 
from  the  case.      Fig.  141   is  a  horizontal  section  through  the 


FIG.  141. 

wheel  and  case,  showing  the  wheel  as  cast  all  in  one  piece. 
It  also  shows  the  chutes  which  control  the  admission  of  water 
and  direct  it  upon  the  floats.  The  wheel  is  surrounded  by  an 
upper  and  a  lower  ring  which  are  united  by  vertical  plates, 
shown  here  as  eight  in  number.  Each  chute  consists  of  a  pair 
of  plates,  one,  called  the  fender  or  guard,  rigidly  joined  to 
the  upper  and  lower  plate,  the  other,  called  the  guide,  turning 
on  a  joint  near  the  periphery  of  the  wheel.  It  is  susceptible 
of  a  movement  sufficient  to  bring  it  into  contact  with  the 


THE    AMERICAN   TURBINE.  289 

adjoining  plate   and  thus  close  the  admission  of  water  to  the 
wheel. 

Fig.  142  is  a  top  view  of  the  upper  plate  or  dome,  showing 
the   mechanism   for   controlling  the   gates.      A  circular  plate 


FIG.   142. 

• 

rotates  on  a  large  hub  on  the  dome  and  carries  a  strong  arm 
to  which  is  attached  a  toothed  segment  gearing  with  a  pinion 
on  the  gate-shaft,  which  is  controlled  by  the  regulator.  The 
circular  plate  carries  also  the  arms  attached  to  the  rotating 
chutes,  whereby  the  influx  openings  can  be  increased  or 
diminished  without  altering  the  direction  or  velocity  of  the 
water  to  the  disadvantage  of  the  wheel. 

This  wheel  is  usually  provided  with  a  draft-tube  and  runs 
upon  a  wooden  step  resting  on  bridge-trees  bolted  to  the 
interior  of  the  tube.  When  placed  in  a  wooden  flume  the 
Weight  is  sustained  by  a  broad  flange  resting  on  the  floor  of  the 
flume  (see  Flume). 

A  ' '  quarter-box  ' '  is  fixed  upon  the  dome  of  the  wheel 
above  the  circular  plate,  forming  a  bearing  for  the  shaft  whereby 


2QO  TURBINES. 

the  wheel  is  accurately  adjusted  in  the  case  and  prevented  from 
binding.  This  box  contains  four  blocks  of  wood,  bearing 
against  the  shaft  endwise  of  their  fibres,  and  adjustable  by 
means  of  set-screws. 

Table  5  gives  the  results  of  certain  tests  of  this  form  of 
wheel  made  at  the  Holyoke  Testing-flume  in  July,  1894. 
They  are  given  on  the  authority  of  Mr.  E.  S.  Waters,  engineer 
of  the  Holyoke  Water-power  Company. 

Later  tests  of  this  wheel  have  shown  a  higher  efficiency ; 
viz.,  a  *test  made  in  September,  1898,  on  a  36-inch  wheel 
showed  an  efficiency 

At  full  discharge  of 82.57  per  cent 

0.92        "  86.27 

0.88        "    •        86.69 

0.83        "  86.76       " 

|          "  85.1 

I  "  78.53       " 

\          "  72-09       " 

These  results  are  avouched  by  Mr.  Waters. 

The  increased  efficiency  when  the  discharge  is  below  the 
maximum  is  thought  to  be  a  peculiar  advantage  of  this  wheel. 
In  its  normal  condition  a  wheel  does  not  run  with  full  discharge. 
It  must  have  some  margin,  some  reserve  of  power  to  meet 
contingencies,  otherwise  it  would  be  liable  to  be  stalled.  It  is 
a  distinct  advantage  to  be  able  to  work  with  best  efficiency  in 
its  normal  running. 

Fig.  143  shows  an  analogous  mode  of  regulating  the  water- 
supply.  The  guides  still  serve  as  gates,  but  are  hinged  near 
the  outer  ends,  the  inner  end  being  susceptible  of  motion  till 
each  guide  touches  its  neighbor  and  so  stops  the  influx  entirely. 
This  movement  is  effected  by  a  toothed  ring  under  the  upper 
guide-plate,  carrying  a  series  of  projections  which  act  upon  the 
outer  extremities  g  of  the  guides.  The  ring  is  rotated  by  a 
pinion  and  shaft  in  the  same  manner  as  the  toothed  segment 
in  Fig.  142.  The  cuts  published  by  the  maker  are  not  clear 


THE  AMERICAN    TURBINE. 


29I 


TABLE  5,  — REPORT  OF  TESTS  OF  A  42-INCH  RIGHT-HAND 
NEW  AMERICAN  TURBINE  AT  THE  TESTING-FLUME  OF 
THE  HOLYOKE  WATER-POWER  COMPANY,  HOLYOKE, 
MASS.,  JULY  14,  1894. 


J 

Proportional  Part 
of 

c 

^ 

! 

|| 

1 

on  the  Whe< 

.1 

i 

w 
£ 

"w 

i 

!i 

$_• 

It 

he  Wheel. 

•o 

•sS 

c  rt 

|||, 

"o 

§| 

2T*  <u  c~ 
-*  Jj  fc£  ^  us 

—  J2  —  t"1  ^ 

t£ 

C 

•Z     £ 

°3 

1. 

Hi 

f* 

"o 

1 

S 

If 

ill!] 

ll 

o.E 

11 

P 

f|| 

Is 

I! 

* 

H" 

£ 

Q 

a"00" 

£ 

w 

33 

I.OOO 

1.014 

16.39 

4 

116.25 

136.40 

200.24 

79-17 

32 

1.008 

16.37 

4 

120.50 

135-60 

200.99 

80.03 

31 

1.004 

16.36 

4 

124.00 

134-97 

200   O8 

80.09 

30 

0-999 

16.33 

4 

128.00 

134-18 

199.56 

80.50 

29 

0.994 

16.33 

4 

132.25 

133-54 

198.08 

80.29 

28 

0.988 

16.28 

3 

i  36  .  oo 

132-53 

194.44 

79.66 

27 

0.710 

0.916 

16.43 

4 

112.25 

123.38 

184.18 

80.31 

26 

0.912 

16.46 

4 

117.50 

122.99 

186.39 

81.38 

25 

0.907 

16.47 

4 

122.25 

122.36 

187.27 

82.13 

24 

0.900 

16.51 

4 

128.25 

121.60 

187-73 

82.65 

23 

0.893 

16.56 

5 

134-80 

120.85 

188.14 

83.09 

22 

0.877 

16.55 

4 

144.00 

118.57 

lSl.37 

81.69 

21 

0.504 

0.798 

16.87 

3 

IIO.OO 

108.99 

164.76 

79-20 

2O 

0-795 

16.74 

3 

113-33 

108.  15 

164.34 

80.24 

19 

o-793 

16.53 

5 

117.00 

107.18 

163.29 

81.47 

18 

0.785 

16.56 

4 

124.00 

106.25 

164.62 

82.70 

17 

0-774 

16.59 

3 

129.33 

104.85 

162.89 

82.77 

16 

0.764 

16.67 

4 

133-75 

103.67 

159-35 

81.50 

15 

0.736 

16.77 

4 

141.75 

IOO.20 

149.58 

78.68 

14 

0.389 

0.700 

17.10 

4 

106.00 

96.17 

I40-73 

75-64 

13 

0.697 

17.04 

3 

113.33 

95-58 

144.28 

78.30 

12 

0.685 

17.11 

4 

120.25 

94.22 

144.91 

79-45 

II 

0.674 

17-13 

4 

125.25 

92.76 

142.40 

79-21 

IO 

0.660 

17-15 

4 

130.00 

90.85 

138.96 

78.83 

9 

0.646 

17.20 

4 

136.00 

Sg.IO 

134.26 

77-43 

8 

0.633 

17-25 

4 

144.50 

87.44 

127.89 

74-94 

7 

0.230 

0.530 

17.42 

4 

102.62 

73-51 

IO0.6I 

69.44 

6 

0.527 

17.44 

4 

108.50 

73.10 

IOI.2O 

70.16 

5 

0.520 

17.48 

4 

113-25 

72.27 

IO0.23 

70.13 

4 

0.509 

17.48 

4 

121.  OO 

70.80 

98.85 

70.60 

3 

0.501 

17.48 

4 

128.75 

69  66 

96.42 

69.99 

2 

0.494 

17-51 

5 

I36.2O 

68.73 

92-73 

68.10 

enough  to  admit  of  a  more  detailed  description.  This  wheel 
has  met  with  some  success.  In  fact  it  is  named  the  "  Success 
Wheel  ' '  by  the  maker.  It  has  not  yielded  quite  so  high  an 


292  TURBINES. 

efficiency  as  the  Swain  or  the  American,  but  it  is  probable  that 
this  does  not  result  from  the  form  of  the  influx  orifices.  The 
maker  claims  an  efficiency  of  80  per  cent  as  the  result  of  tests 
on  this  wheel. 


FIG.  143. 

The  Risdon  Wheel  is  shown  in  vertical  section  with  its 
attachments  in  Fig.  144,  in  exterior  view  in  Fig.  145,  and  the 
wheel  detached  from  the  case  appears  in  Fig.  146.  A  is  the 
wheel,  which  is  cast  in  a  single  piece;  B B  the  guides,  which  are 
cast  in  one  piece  with  the  guide-plate  R.  Three  of  the  guides 
are  heavier  than  the  others  and  support  the  pieces  F  F  which 
sustain  the  crown-plate  £,  and  have  the  slots  G  to  admit  of  the 
movement  of  the  gate.  In  other  words,  the  supports  FFrest  on 
the  thick  guides,  straddle  the  gate,  and  sustain  the  crown-plate. 
This  latter  is  circular  and  makes  a  water-tight  joint  with  the 
cylindrical  gate  C  by  means  of  the  packing-ring  H.  From 
the  crown-plate  E  rises  the  cylinder  //  enclosing  the  shaft  and 
forming,  at  the  upper  part,  the  bearing  K K.  Outside  of  //is 


THE   RISDON    WHEEL, 


293 


a  second  cylinder  which  fits  II  closely  at  its  lower  end,  and  at 
the  lower  end  is  attached  to  the  gate  by  the  arms  L  L,  and  at 
the  upper  part  is  attached  to  the  piston  ooy  which  is  fitted  to 
the  interior  of  the  cylinder  P.  The  space  oo  within  the  cylin- 
der P  communicates  with  the  interior  of  the  wheel  through  the 
orifices  Q  Q,  while  the  lower  side  of  the  piston  is  exposed  to 


FIG.   144. 

the  pressure  due  the  head,  which  balances  the  weight  of  the 
gate,  the  size  of  P  being  fixed  with  that  view.  The  cylinder 
outside  of  //  carries  a  toothed  rack,  gearing  with  the  pinion  M, 
whereby  the  gate  is  raised  and  lowered.  The  shaft  of  the 
pinion  M  is  supported  by  the  standard  N  bolted  to  the  crown- 


294  TURBINES. 

plate.  DD  are  projections  or  fingers  attached  to  the  gate 
which  fit  between  the  guides  and  serve  to  contract  the  chutes 
as  the  gate  descends.  Fis  the  wheel-shaft,  and  J-Fthe  shaft 


FIG.  145. 

for  operating  the  gate.  U  is  the  wooden  step  of  the  shaft 
resting  upon  the  cross-tree  T.  S  is  a  short  pipe  discharging 
the  water  below  the  level  of  the  lower  pooi.  This  wheel  sits 


THE  RISDON    WHEEL.  2Q$ 

inside  a  wooden  or  iron  flume  in  which  the  water  is  under  the 
pressure  due  the  head. 

From  the  shape  of  the  buckets  it  will  appear  that  the  dis- 
charge of  this  wheel  is  mainly  downward  through  orifices  radial 
to  the  wheel,  the  inner  end  of  the  orifice  of  discharge  moving 
not  more  than  half  as  fast  as  the  outer,  a  disposition  clearly 
inconsistent  with  the  highest  efficiency.  If  we  determine  the 
speed  of  best  efficiency  of  a  wheel,  and  then  reduce  that  speed 


FIG.  146. 

or 


one-half,  we  shall  reduce  the  efficiency  as  much  as  one-third 
more.  Making  all  due  allowance  for  the  effect  of  centrifugal 
force,  it  is  plain  that  if  the  water  near  the  outer  part  of  the 
orifice  acts  with  best  efficiency,  the  water  toward  the  inner  end 
must  act  with  diminished  efficiency.  The  maker  of  this  wheel 
claims  an  efficiency  of  over  91  per  cent,  and  professes  to  have 
the  certificate  of  an  expert  to  verify  this  claim. 

Fig.  147  is  a  section  of  the  "  Victor  wheel,"  made  by  Still- 
well  Bierce  &  Co.  of  Dayton,  Ohio.  Wis  the  solid  part  of  the 
wheel  which  revolves  with  the  floats  FF,  the  shaft  S,  and  the 


296 


TU 'RBINES. 


FIG.   147, 


DUPLEX    WHEEL.  297 

ring  R.  gg  are  the  guides  attached  to  fixed  plates.  G  is  the 
cylindrical  gate  to  which  are  attached  the  toothed  uprights  L  L 
operated  by  spur-gears  on  the  shaft  n,  one  end  of  which  carries 
a  bevel-gear  for  controlling  the  gate  by  means  of  a  hand-wheel 
acting  through  the  small  shaft  P,  the  other  a  wheel  through 
which  the  regulator  acts.  The  uprights  LL  rise  through  the 
crown-plate  C  into  hollow  chambers  DD.  The  reader  will 
notice  the  internally  projecting  lip  on  the  bottom  of  the  gate 
for  giving  the  desired  direction  to  the  water  entering  the  wheel. 
M  is  the  foot  on  the  bottom  of  the  shaft,  and  T  the  wooden 
step  on  which  it  rests,  t  is  a  cross-tree  fixed  to  the  bottom  of 
the  draft-tube  d,  and  sustaining  the  socket  for  the  step  T. 
Only  the  outlines  of  two  buckets  are  shown  in  the  drawing ; 
the  projections  of  the  remainder  are  not  shown.  The  discharge 
is  all  around  the  free  edge  of  the  bucket,  so  that  this  wheel  has 
an  inward,  a  downward,  and  an  outward  discharge. 

Tests  of  this  wheel  at  the  Holyoke  Company's  flume  have 
given  an  efficiency 

For  full  discharge  of 80  to  82  per  cent 

|  "  78  to  8 1 

I          "  75  to  77       » 

f          "  70  to  72       " 

£  "  63  to  64        " 

Duplex  Wheel. — Fig.  148  shows  an  arrangement  which 
has  met  with  some  application,  designed  to  use  a  varying 
quantity  of  water  with  good  effect.  It  consists  of  a  double 
wheel,  that  is,  a  wheel  with  two  sets  of  floats  and  two  sets  of 
guides,  each  controlled  by  a  separate  gate,  and  susceptible  of 
being  used  separately  or  in  combination,  //are  the  floats,  gg 
the  guides,  and  GG  the  gate  of  the  outer  wheel  w\  f'f  the 
floats,  g ' g'  the  guides,  and  G'G'  the  gate  of  the  inner  wheel  w' . 
The  gate  of  the  outer  wheel  closes  by  rising,  that  of  the  inner 
by  descending.  When  the  water  is  low,  the  gate  G  of  the 
outer  wheel  is  closed,  and  the  water  acts  only  on  the  floats/'; 
as  the  flow  increases  the  inner  gate  is  closed,  the  outer  gate 


TURBINES. 


opened,  and  the  water  acts  on  the  floats/.  In  high  stages  of 
the  stream  both  gates  are  open.  The  shaft  runs  on  a  suspen- 
sion bearing  near  the  top  and  should  have  a  guide-bearing  or 
quarter-box  near  the  wheel,  above  or  below,  to  centre  the 


FIG.   148.. 

wheel  in  its  case.      The  form  of  the  buckets  and  guides  appears 
in  dotted  lines. 

This  combination  will,  no  doubt,  use  a  quantity  of  water 
equal  to  the  capacity  of  the  inner  wheel,  with  greater  economy 
than  the  same  quantity  of  water  could  be  used  by  a  single 
Avheel  of  capacity  equal  to  that  of  the  two,  and  it  would,  no 
<doubt,  give  a  reasonably  good  result  with  the  outer  gate  alone 


DUPLEX    WHEEL.  299 

open.  The  combination  presents  in  an  exaggerated  degree 
the  defect  already  pointed  out,  viz. :  if  the  velocity  is  such 
that  the  outer  wheel  gives  its  best  effect,  it  will  be  much  too 
slow  for  the  inner  wheel.  Moreover,  when  the  inner  wheel  is 
in  use  and  the  outer  gate  closed,  the  rotation  of  the  outer  wheel 
is  an  additional  burden  of  useless  work  laid  upon  the  inner 
wheel.  The  most  serious  defect  of  the  combination,  however, 
is  this:  in  the  arrangement  shown,  neither  of  the  wheels  acting 
by  itself  would  give  a  good  result  on  part  gate.  Wheels  of 
this  form  are  by  no  means  new.  They  have  given  good  results 
with  full  discharge,  but  their  great  defect  has  been  the  impossi- 
bility of  a  good  result  at  part  gate.  The  only  successful  mode 
of  regulation  has  been  by  a  separate  gate  for  such  guide  open- 
ing, but  no  approach  to  economical  regulation  is  possible  with 
gates  of  the  form  shown.  It 'must  be  observed  that  the  gate  is 
outside  of  both  guides  and  floats,  and  that  the  water  passes 
through  a  chamber  of  some  size  before  reaching  the  guides. 
A  serious  loss  of  head  always  occurs  when  water  passes  through 
a  narrow  opening  from  one  chamber  to  another.  The  defects 
of  this  arrangement  are  similar  to  what  would  be  met  with  in 
attempting  to  regulate  the  supply  of  water  to  a  turbine  by  a 
throttle-gate  in  the  penstock. 

There  are  other  forms  of  turbine  which  the  writer  would  be 
glad  to  describe  and  consider  if  he  could  obtain  the  necessary 
data.  Prominent  among  these  is  the  Leffel  wheel,  made  at 
Springfield,  Ohio,  which  has  met  with  extended  application  in 
the  Western  States  and  is  not  unknown  in  the  Eastern  section, 
which  facts  entitle  us  to  presume  that  it  has  points  of  merit. 
But  nothing  can  be  learned  from  the  numerous  publications  of 
the  makers  as  to  the  construction  of  the  wheel  or  the  manner 
in  which  the  water  acts  to  propel  it.  Equally  reticent  are  the 
makers  as  to  the  efficiency  of  the  wheel.  They  do  not  believe 
in  tests  and  assume  that  their  readers  attach  no  importance  to 
them.  Their  publications  abound  in  vociferous  assurances  of 
the  excellence  of  the  wheel,  but  neither  give  the  intending 


30O  TURBINES. 

purchaser  the  means  of  judging  for  himself  nor  furnish  him  with 
the  results  of  exact  experiments  as  to  its  performance. 

The  Hercules  Wheel,  so  called,  made  by  the  Holyoke 
Machine  Company  at  Holyoke,  Mass.,  is  very  extensively  used 
in  New  England  and  the  Middle  States.  The  makers  issue  a 
very  neat  catalogue  giving  illustrations  and  description  of  all 
the  appurtenances  and  attachments  of  the  wheel,  but  the 
inquiring  reader  will  search  it  in  vain  for  any  information  as  to 
the  construction  of  the  wheel,  the  forms  of  the  floats  and 
guides,  the  regulation  of  the  water,  or  its  mode  of  action. 
Results  of  experiments  upon  this  wheel  are  published,  which 
are  of  commercial  interest,  but  such  information  has  no  scientific 
interest  unless  accompanied  by  a  knowledge  of  the  construction 
of  the  wheel  and  the  manner  in  which  the  water  acts  thereon. 

The  Hurdy  Gurdy  Wheel. — We  now  come  to  a  form  of 
wheel  which  can  hardly  be  classed  as  a  turbine,  since  it  cannot, 
generally,  like  the  latter  be  placed  below  the  level  of  the 
tailwater,  neither  can  it  act  in  connection  with  a  draft-tube. 
It  consists  of  a  series  of  cup-shaped  vanes  attached  to  the 
periphery  of  a  wheel  and  acted  on  by  a  jet  of  water.  It  is 
usually  mounted  on  a  horizontal  shaft,  which  carries  the  organs 
for  transmitting  motion,  and  in  that  form  is  probably  the 
simplest  combination  for  the  development  of  water-power  that 
can  be  devised.  It  is  an  impulse-wheel  in  the  most  elementary 
form,  neither  reaction  nor  direct  weight  contributing  anything 
to  the  result. 

Fig.  149  is  an  elevation  of  the  wheel  in  a  plane  transverse 
to  the  shaft,  Fig.  150,  parallel  to  the  same.  The  wheel  is  here 
shown  enclosed  in  a  wooden  case,  to  protect  the  surroundings 
from  the  spray  which  could  not  fail  to  be  plentifully  distributed 
by  such  a  wheel.  Fig.  149^  is  a  section  of  the  vane  by  a 
plane  tangential  to  the  wheel;  Fig.  149^,  a  section  perpendicu- 
lar to  a.  It  is  shaped  so  as  to  divide  the  stream  and  throw  the 
parts  clear  of  the  adjoining  vane,  and  cannot,  therefore,  exactly 
reverse  the  direction  of  the  stream,  but  it  probably  realizes  this 


THE  HURDY  GURDY    WHEEL. 


301 


3O2  TURBINES. 

condition  of  perfect  efficiency  as  closely  as  is  possible  in  any 
wheel. 

The  simplicity  of  this  wheel  is  only  preserved  by  limiting 
the  number  of  nozzles  to  two  or  three,  or  at  most  four.  To 
attempt  to  apply  the  water  by  a  series  of  nozzles  extending  all 
round  the  periphery  would,  with  the  necessary  regulating 
mechanism,  lead  to  as  complex  a  form  as  in  any  existing  wheel. 
For  this  reason  the  wheel  cannot  give  a  large  amount  of  power 


FIG.  i49«.  FIG.  149^. 

except  with  a  great  head.  The  simplicity  and  cheapness  of 
the  wheel,  however,  allow  of  its  duplication  to  any  extent, 
either  by  placing  a  number  of  wheels  upon  the  same  shaft,  or 
by  providing  a  wheel  for  each  machine  or  group  of  machines. 
This  wheel  must  not  only  be  placed  above  the  tailwater,  but 
high  enough  above  to  be  free  from  any  risk  of  interference  by 
backwater.  The  head  thus  sacrificed  would,  on  any  moderate 
fall,  amount  to  too  large  a  proportion  of  the  whole  to  be 
economical.  For  these  reasons  the  application  of  the  wheel  is 
not  to  be  recommended  for  heads  under  50  feet,  nor  even  in 
that  case  when  the  head  is  liable  to  great  variation  from  back- 
water. These  conditions  restrict  the  application  of  the  wheel 
to  special  cases. 

The  regulation  of  the  supply  of  water  and  the  speed  of  these 
wheels  is  sometimes  attempted  by  means  of  cocks  in  the  pipes 
leading  to  the  nozzles.  For  a  wheel  with  four  nozzles  this 
method  would  not  be  inconsistent  with  a  good  result  at  full 
discharge,  and  at  three-fourths,  one-half,  and  one-fourth  of 
same.  But  the  water  from  the  pipe  which  was  undergoing 
contraction  would  act  at  a  great  disadvantage  on  account  of 


THE  HURDY  GURDY    WHEEL. 


303 


the  loss  of  head  incident  to  the  action  of  the  cock.  For  a 
wheel  propelled  by  a  single  nozzle  as  at  Fig.  149  this  mode  of 
regulation  would  be  wholly  inapplicable.  The  speed  of  the 
vanes  is  fixed  by  the  application  or  use  made  of  the  power  and 
may  be  considered  invariable.  This  velocity  we  may  take  as 
that  of  greatest  efficiency,  viz.,  one-half  that  due  the  full  head 


acting  on  the  wheel.  In  the  arrangement  of  Fig.  149,  if  the 
supply  be  controlled  wholly  by  the  gate  there  shown,  the 
issuing  stream  will  be  of  the  full  size  of  the  nozzle  efflux, 
irrespective  of  the  extent  to  which  the  gate  is  closed.  The 
gate  acts  to  diminish  the  pressure  in  the  space  between  the 


304  TURBINES. 

gate  and  efflux,  and  consequently  the  velocity  of  the  issuing 
stream.  Equation  39  gives  for  the  energy  exerted  on  a  cup- 
shaped  vane  moving  with  the  velocity  u,  under  the  action  of  a 
stream  of  water,  of  cross-section  a,  with  the  velocity  v, 

2u(v  —  u} 
Pit  =  wav  — — -. 


<w  being  the  weight  of  a  cubic  foot  of  water.      Suppose  n  to  be 
the  velocity  of  maximum  efficiency,  viz.,  u  =  -.      If  now  we 

suppose  the  velocity  v  to  be  reduced  by  one-fourth,  u  remain- 
ing unchanged,  we  have 

Pu  -  \wavV^V  "*V'  =  \wav  X  -  —  =  \Qu>  XP  =  ^Qwh. 

o  o 

The  diminution  of  the  velocity  by  one-fourth,  therefore, 
diminishes  the  power  by  five-eighths,  and  the  efficiency  by  one- 
half. 

Diminishing  v  by  one-half  reduces  Pu  to  o. 

It  is  understood  that  this  difficulty  is,  in  some  degree, 
overcome  by  a  series  of  nozzle-tips  of  varying  sizes,  these  being 
changed  according  to  the  requirements  of  the  power.  It  is 
manifest,  however,  that  no  efficient  regulation  to  meet  the 
requirements  of  a  varying  load  could  be  effected  by  such 
means.  The  only  economical  mode  of  controlling  the  flow 
from  the  nozzle  is  by  a  device  to  contract  the  stream  at  its 
efflux  from  the  same ;  varying  the  cross-section  of  the  issuing 
stream,  but  not  its  velocity. 

Wheels  of  this  construction  were  tested  in  1896  at  the 
Ohio  State  University,  at  Columbus,  Ohio,  and  yielded  under 
a  head  of  162  feet,  according  to  certificates  of  officers  of  that 
institution,  a  maximum  efficiency  of  92  per  cent,  which  state- 
ment is  not  beyond  belief.  Tests  of  these  wheels  under  low 
or  medium  heads  are  liable  to  be  misleading.  The  head  on 
•which  the  efficiency  is  computed  is  usually  taken  as  limited  by 


THE  HURDY  GURDY    WHEEL.  305 

the  height  at  which  the  stream  strikes  the  vanes,  a  mode  of 
computation  which  does  not  give  a  fair  basis  of  comparison 
between  this  wheel  and  others.  This  wheel  stands  above  the 
tailwater  or  lower  pool,  and  often,  when  backwater  is  to  be 
expected,  many  feet  above  the  same;  whereas  another  wheel 
would  stand  below  the  same  level,  and  utilize  the  entire  head 
at  all  times.  Obviously  the  head  to  be  used  in  these  computa- 
tions should  be  the  entire  head  available  between  the  upper 
and  lower  pools,  with  no  deduction  for  that  portion  of  the  head 
which  has  to  be  sacrificed  to  the  practical  form  and  character 
of  the  wheel. 


CHAPTER   XV. 
APPENDAGES   AND   ATTACHMENTS   OF  TURBINES. 

The  Case. — This  term  is  usually  applied  to  the  fixed  parts 
sustaining  the  guides  and  gate  or  gates,  which  the  maker 
furnishes  with  the  wheel  and  is  regarded  as  a  part  of  the  same. 
It  embraces  the  plate  or  disk  which  supports  the  guides  and  a 
plate  which  relieves  the  wheel  of  the  pressure  of  the  water.  In 
the  Boyden  wheel,  Fig.  136,  these  two  plates  are  the  same. 
This  latter  plate  contains  a  stuffing-box  through  which  the  shaft 
passes,  or,  as  in  the  Boyden  wheel,  a  pipe  reaching  above  the 
water.  The  case  usually  carries  the  mechanism  for  manoeu- 
vring the  gate,  and  often  the  step  on  which  the  shaft  runs. 
The  case  is  usually  enclosed  in  a  flume  in  communication  with 
the  upper  level,  and  in  most  modern  wheels  contains  the  guide- 
bearing  which  centres  the  wheel  in  the  case.  In  every  form 
of  the  turbine,  properly  so  called,  there  are  inevitably  two 
annular  openings  between  the  wheel  and  case  through  which 
the  water  is  free  to  pass  under  a  pressure  not  greatly  less  than 
that  of  the  full  head  acting  on  the  wheel.  With  the  most 
accurate  adjustment  of  the  guide-bearing  this  opening  can 
hardly  be  less  than  £  inch  in  width.  For  a  wheel  6  feet  in 
diameter  there  is  a  space  of  2  X  6?r  x  -^V  =  0.393  square  foot 
for  the  free  escape  of  water,  which  "under  a  head  of  20  feet 
might  occasion  a  loss  of  5  or  6  cubic  feet  per  second.  There 
appears  to  be  no  means  in  use  for  obviating  this  waste,  since, 
if  the  clearance  were  made  narrower,  maladjustment  or 
derangement  of  the  guide-bearing  might  cause  the  wheel  to 
bind.  From  the  rapid  motion,  anything  in  the  nature  of  a 

306 


THE   DRAFT-TUBE. 


307 


FIG.  151. 


packing-ring  would  waste  more  power  in  friction  than  it  could 
save  in  water. 

A  patent  was  issued  to  the  writer  under  date  of  January 
19,  1886,  on  the  combination  indicated  in  Fig.  151,  in  which 
W'vs,  supposed  to  pertain  to  the 
revolving  wheel,  C  to  the  station- 
ary case,  with  an  interval  between 
them  as  small  as  will  permit  the 
wheel  to  run.  A  ring  R  rests 
upon  a  seat  formed  on  the  case 
and  encircles  the  wheel  with  a 
clearance  much  less  than  is 
necessary  between  the  wheel  and 
case.  This  ring  is  held  upon  its 
seat  by  the  pressure  of  the  water. 
Any  movement  of  the  wheel  by  the  derangement  of  the  guide- 
bearing  merely  alters  the  position  of  the  ring  on  its  seat;  and 
while  a  clearance  of  %  inch  might  be  necessary  between  the 
wheel  and  its  case,  a  clearance  of  -^  would  be  ample  between 
the  wheel  and  ring. 

The  Draft-tube. — The  head  or  fall  acting  on  a  wheel  is 
determined  by  physical  conditions.  It  is  the  elevation  of  the 
upper  pool  or  upper  level,  otherwise  called  the  headwater, 
above  the  lower  pool  or  lower  level,  otherwise  called  the  tail- 
water.  A  wheel  set  any  number  of  feet  above  the  latter  and 
discharging  into  the  air  loses  so  many  feet  of  the  head ;  but  if 
it  discharges  through  a  vertical  pipe  whose  effiux  is  below  the 
lower  level,  the  water  will  free  the  pipe  from  air,  and  the 
pressure  against  which  the  water  issues  from  the  buckets  will 
be  reduced  by  the  exact  equivalent  of  that  part  of  the  head 
between  the  centre  of  the  discharge-orifices  and  the  tailwater. 
In  other  words,  the  draft-tube  renders  the  entire  head  available, 
though  the  wheel  may  set  considerably  above  the  lower  level. 
Of  course  this  height  cannot  exceed  that  corresponding  to  the 
atmospheric  pressure,  which  at  the  sea-level  is  about  34  feet 
as  an  average,  otherwise  there  would  be  a  vacuum  immediately 


308 

below  the  wheel,  and  a  part  of  the  head  would  be  lost.  In 
practice  the  draft-head  never  reaches  this  limit  or  closely 
approaches  it;  27  feet  may  be  considered  the  extreme  height, 
and  it  is  usually  much  less. 

It  is  not  easy,  at  first  view,  to  understand  how  the  water 
issuing  from  the  discharge-orifices  of  the  wheel  operates  to 
expel  the  air  from  the  draft-tube.  The  process  is  very  simple. 
When  the  draft-tube  is  empty,  the  surface  of  the  water  stands 
at  the  same  level  inside  as  outside,  viz.,  the  level  of  the  tail- 
water.  When  the  gate  is  raised,  streams  of  water  fall  inside 
the  tube,  and,  striking  the  surface,  beat  it  into  foam,  i.e.,  fill 
it  with  minute  bubbles  of  air  and  create  a  current  which  carries 
the  water  in  that  condition  downward,  and  the  bubbles  rise 
outside  the  tube.  The  smallest  bubbles  of  air  do  not  rise  in 
still  water  with  a  velocity  of  more  than  9  to  12  inches  per 
second;  a  velocity  greater  than  the  latter  will  carry  them 
downward.  In  this  manner  the  air  is  entirely  expelled  from 
the  tube. 

The  pressure  on  the  draft-tube  is  from  without  inward,  and 
it  must  be  formed  to  withstand  such  a  pressure.  At  the  foot 
of  the  tube,  that  is,  at  the  surface  of  the  tailwater,  there  is  no 
pressure  outward  or  inward.  At  any  point  above  the  tailwater 
the  pressure  is  inward  and  equal  to  that  due  the  neight  of  the 
said  point. 

By  means  of  the  draft-tube,  wheels  on  a  vertical  shaft  may 
be  placed  so  as  to  be  accessible  for  examination  and  repairs 
without  draining  the  pit.  With  this  view  it  is  advisable  to  fit 
the  tube  with  a  manhole  for  admission.  A  cock  is  sometimes 
inserted  in  order  to  fill  the  tube  with  air  and  free  it  of  water 
before  opening  the  manhole.  As  to  wheels  on  horizontal 
shafts,  it  is  only  through  the  draft-tube  that  their  use  is  possi- 
ble. Sucn  a  shaft  must  carry  the  gear  or  pulley  for  transmitting 
motion,  and  these  organs  could  not  operate  below  the  level  of 
the  tailwater.  It  is  not  too  much  to  say  that  the  adoption  of 
the  draft-tube  marks  a  distinct  era  in  the  development  of  the 
appliances  of  water-power.  By  giving  a  ' '  flare  ' '  to  the  draft- 


THE  DIFFUSER.  309 

tube,  causing  it  to  expand  downward,  we  may  induce  the  same 
action  as  occurs  in  the  diffuser  (next  paragraph)  and  thereby 
diminish  to  some  extent  the  loss  of  head  due  to  the  velocity 
with  which  the  water  leaves  the  wheel.  , 

The  Diffuser  is  an  expanding  passage  through  which  the 
water  passes  after  leaving  the  wheel.  As  applied  to  an 
outward-flow  turbine  it  takes  the  form  of  Fig.  152.  To  an 
inward-flow  wheel  it  is  not  readily  applicable  unless  the  wheel 
works  with  a  draft-tube,  in  which  case  the  diffuser  consists  in 
a  conical  form  of  the  latter,  widening  downward.  The  diffuser 
is  the  invention  of  Mr.  U.  A.  Boyden,  and  is  especially 
applicable  to  the  Boyden  wheel.  Its  purpose  is  to  employ  the 
momentum  with  which  the  water  leaves  the  wheel,  in  diminish- 
ing the  back  pressure  or  the  pressure  acting  against  the  dis- 
charge. Its  practical  effect  is  to  slightly  increase  the  head 
acting  on  the  "wheel.  The  extent  to  which  it  increases  the 
head  is  represented  by  the  head  due  the  velocity  with  which 
the  water  leaves  the  wheel  diminished  by  the  head  due  the 
velocity  with  which  it  leaves  the  diffuser. 

The  effect  of  the  diffuser  can  be  best  expressed  in  the 
language  of  Mr.  J.  B.  Francis,*  with  reference  to  the  case  of 
Fig.  152:  "On  leaving  the  wheel,  it  [the  water]  necessarily 
has  a  considerable  velocity,  which  would  involve  a  correspond- 
ing loss  of  power  but  for  the  diffuser,  which  utilizes  a  portion 
of  it.  When  operating  under  a  fall  of  33  feet  and  the  speed- 
gate  raised  to  its  full  height,  this  wheel  discharges  about  219 
cubic  feet  of  water  per  second.  The  area  of  the  annular  space 
o,  0,  o,  o,  Fig.  152,  where  the  water  enters  the  diffuser,  is 
0.802  X  8./927T  =  22.152  square  feet;  and  if  the  stream 
passes  through  this  section  radially,  its  mean  velocity  must  be 

2  IQ 

—  =  0.886  feet  per  second,   which  is  due  to   a  head  of 

22.152 

1.519  feet.  The  area  of  the  annular  space/,  p,  p,  p,  where 
the  water  leaves  the  diffuser,  is  1.5  X  15  333*  =  72.255  square 

*  Lowell  Hydraulic  Experiments,  1868,  p.  231. 


3io 


TUBBINES. 


THE  FLUME.  311 

feet,  and  the  mean  velocity  z^~ :  =  3.031   feet  per  second, 

which  is  due  to  a  head  of  o.  143  feet.  According  to  this,  the 
saving  of  head  due  to  the  diffuser  is  1.519  —  0.143  =  I-3/6 

feet,  being  - — —  ,  or  about  4|  per  cent  of  the  head  avail- 
able without  the  diffuser,  which  is  equivalent  to  a  gain  in  the 
coefficient  of  useful  effect  to  the  same  extent.  .  .  .  Experi- 
ments on  the  same  turbine  with  and  without  a  diffuser  have 
shown  a  gain  due  to  the  latter  of  about  3  per  cent  in  the  coeffi- 
cient of  useful  effect.  The  diffuser  adds  to  the  coefficient  of 
useful  effect  by  increasing  the  velocity  of  the  water  passing 
through  the  wheel,  and  it  must  of  course  increase  the  quantity 
of  water  discharged  in  the  same  proportion.  If  it  increases  the 
available  head  3  per  cent,  the  velocity,  which  varies  as  the 
square  root  of  the  head,  must  be  increased  about  i£  per  cent, 
and  the  quantity  discharged  must  be  increased  in  the  same  pro- 
portion. The  power  of  the  wheel,  which  varies  as  the  product 
of  the  head  into  the  quantity  of  water  discharged,  must  be 
increased  about  4^  per  cent. ' ' 

The  Flume. — In  order  to  cause  the  water  to  act  upon  the 
wheel,  the  latter  is  usually  enclosed  in  a  chamber  communicat- 
ing with  the  upper  level  by  a  penstock  or  head-race,  and 
with  the  lower  level  by  a  tail-race,  which  it  enters  by  passing 
through  the  wheel.  This  chamber  is  called  the  flume.  The 
outward-discharge  turbine  does  not  require  a  flume  properly  so 
called,  but,  as  very  few  of  that  class  of  wheels  are  now  built,  we 
may  regard  the  flume  as  a  necessary  appendage  of  the  turbine. 
The  flume  may  be  of  wood,  iron,  stone,  or  a  combination  of 
these  materials,  the  choice  depending  very  much  upon  the  head. 
With  a  head  not  exceeding  15  feet,  wood  or  a  combination  of 
wood  and  stone  will  generally  be  found  preferable,  and  with 
the  aid  of  draft-tubes  the  same  construction  may  be  employed 
up  to  a  head  of  30  feet.  Above  this  limit  iron  is  generally  to 
be  preferred. 

Fig-  153  is  a  vertical  cross-section  of  a  flume  for  a  double 


312 


TUKBINES. 


turbine  on  a  horizontal  shaft  under  a  head  of  15  to  30  feet. 
For  a  head  less  than  1 5  feet  the  arrangement  would  be  in  no 
way  different  except  in  the  absence  of  the  upper  deck.  The 
floor-timbers  of  the  flume  rest  upon  the  walls  of  the  race.  Into 


these  are  mortised  the  uprights,  and  the  latter  are  joined  at  the 
top  by  the  upper  cross-timbers  or  ties  which  sustain  the  deck. 
These  connections  are  made  by  dovetailed  joints  and  wedges, 
tomeet  the  pressure  tending  to  lift  the  deck.  The  floor  of  the 


THE   FLUME. 


313 


flume  is  represented  at  Fig.  1 54.  The  two  central  floor-tim- 
bers cannot  extend  across  the  flume,  but  are  terminated  by  the 
timbers  EE,  which,  together  with  the  two  cross-timbers  into 
which  they  are  mortised,  form  a  square  opening  large  enough 
to  admit  the  draft-tube.  This  is  reduced  to  an  octagonal 
opening  by  the  corner  blocks  BB,  confined  by  bolts.  The 
planking  overlaps  a  little  and  is  finished  to  a  circle  conforming 


J 


EEU 


FIG.  154- 

to  the  draft-tube,  which  rests  thereon  by  a  broad  flange.  The 
shaft  passes  through  stuffing-boxes  in  the  side  of  the  flume  and 
rests  in  bearings  outside  the  flume,  which  are  supported  by 
timbers  bolted  to  the  uprights.  The  small  shafts  for  manipu- 
lating the  gates  pass  through  stuffing-boxes  in  the  top  of  the 
flume. 

Fig-  155  is  a  longitudinal  section  showing  the  tail-race  and 
penstock.     The  latter  takes  smaller  dimensions  both  in  height 


TURBINES. 


THE  FLUME.  315 

and  width  from  the  flume,  to  the  source  of  supply.  At  the 
down-stream  end  of  the  flume  the  thrust  tending  to  push  the 
uprights  out  of  place  cannot  be  met  in  the  same  way  as  at  the 
sides.  The  floor-plank  are  extended  a  couple  of  feet,  and  on 
the  outer  ends  are  bolted  the  timbers  A  A  which  sustain  the 
pressure  against  the  uprights.  The  pull  upon  the  uprights  is 
here  met  by  iron  rods  joining  the  deck  to  the  floor. 

At  the  influx  of  the  penstock  it  is  usually  necessary  to  make 
a  water-tight  connection  with  the  masonry  of  the  dam,  or  canal 
wall.  This  is  shown  at  Fig.  155^,  where  the  plank  are  spiked 
to  timbers  built  into  the  masonry.  The  walls  of  the  flume  are 
sometimes  of  masonry,  and  the  floor  of  timber.  In  this  case 
the  ends  of  the  cross-timbers  are  firmly  built  into  the  masonry, 
and  the  joint  between  the  plank  and  the  latter  may  be  calked 
with  oakum  and  paid  with  tar.  The  joint  at  the  ends  of  the 
plank  is  arranged  as  at  Fig.  1550.  The  end  cross-timber  is 
partly  imbedded  in  the  masonry  and  confined  thereto  by  bolts, 
the  joint  at  the  ends  of  the  plank  being  calked  as  before. 

The  advantage  of  mounting  two  wheels  on  a  horizontal 
shaft  consists  in  mutually  neutralizing  the  thrust.  This,  how- 
ever, only  occurs  completely  when  both  wheels  are  running  at 
equal  gate.  A  thrust-bearing  cannot  be  dispensed  with  in  this 
case,  as  one  wheel  is  liable  to  run  at  full  gate  while  the  other 
has  its  gate  wholly  or  partly  closed.  . . 

Fig.  156  shows  a  very  neat  arrangement  of  a  cast-iron 
quarter-turn  flume  for  a  high  head.  The  flume,  by  means  of  a 
flange  strengthened  with  gussets,  rests  on  iron  beams  spanning 
the  tail-race,  or  wheel-pit.  The  quarter-turn  is  made  in  two 
halves,  and  has  a  neck  strengthened  with  gussets  through 
which  the  shaft  passes  by  a  stuffing-box.  This  neck  carries  a 
broad  flange  to  which  is  bolted  the  bridge-tree  for  sustaining 
the  crown-gears,  which  give  motion  to  the  horizontal  shaft 
carrying  a  pulley  and  belt  for  delivering  the  power.  To  the 
horizontal  end  of  the  quarter-turn  is  bolted  a  very  short  length 
of  pipe  or,  more  properly,  a  ring,  pierced  with  rivet-holes  for 
attaching  the  wrought-iron  penstock.  A  manhole  appears  in 


FIG.   156. 


THE  FLUME. 


317 


the  side  of  the  flume  for  admission  to  the  interior.  In  this  form 
the  word  "flume  "  is  usually  applied  to  the  chamber  enclosing 
the  wheel,  the  remainder  of  the  pipe  being  known  as  the  pen- 
stock. This  arrangement  is  presented  by  the  Rodney  Hunt 
Company  of  Orange,  Mass. 

In  adopting  this  cut  the  writer  feels  obliged  to  disclaim  the 
method  therein  indicated  of  constructing  the  arch  over  the  tail- 


FIG.  157. 

race.  The  bricks  are  shown  as  laid  flatwise,  which  would  be 
as  unworkmanlike  as  putting  bricks  on  end  in  a  vertical  wall. 
Bricks  in  an  arch  are  always  laid  with  their  ends  or  their  edges 
to  the  soffit,  and  so  as  to  receive  the  pressure  on  their  broad- 
est faces. 

Fig.    157   shows  a  flume  of  stone,   iron,   and   wood,  viz., 
stone  side  walls,  iron  beams,  and  wooden  floor,  for  a  pair  of 


318  TURBINES 

turbines  to  drive  a  pulp-grinder.  The  main  shaft  goes  through 
a  stuffing-box  built  into  the  wall  and  rests  in  a  bearing  in  the 
same  opening.  This  figure  is  taken  from  the  catalogue  of 
S.  Morgan  Smith  of  York,  Pa.  The  hand-wheel  shaft  for 
manipulating  the  gates  also  passes  through  a  stuffing-box; 
though,  the  flume  being  open  at  the  top,  there  is  nothing  to 
hinder  it  from  entering  freely  from  above.  When  such  a  struc- 
ture rests  upon  anything  but  good  sound  rock  it  should  have  a 
substantial  flooring  of  timber  and  planking,  not  only  to  prevent 
settlement  of  the  masonry,  but  to  protect  the  bottom  from  the 
wash  of  the  discharge. 

Step  and  Suspension  Bearing. — A  bearing  to  support  the 
shaft,  wheel,  crown-gear,  and  attachments  while  in  rapid 
motion  is  no  light  problem  in  mechanics,  though  not  the  most 
difficult  form  of  the  problem.  This  occurs  in  the  thrust-bear- 
ing of  the  steam-propeller  which  sustains  the  entire  pressure 
that  drives  the  vessel  through  the  water,  often  amounting  to 
50  tons  acting  through  a  shaft  in  rapid  rotation.  This  strain 
is  successfully  met  by  a  thrust-bearing,  Fig.  212,  which  con- 
sists of  a  series  of  deep  grooves  cut  on  the  shaft  near  the  end, 
forming  a  series  of  collars  which  bear  against  corresponding 
surfaces  in  a  hollow  box.  Often  the  external  collars  are  formed 
of  soft  metal,  consisting  mainly  of  tin,  which  is  poured  into  the 
hollow  box  and  forms  a  casting  conforming  to  the  grooves  on 
the  shaft.  This  method  having  been  successfully  employed  for 
the  thrust-bearings  of  screw-steamers,  there  can  of  course  be  no 
doubt  as  to  its  applicability  to  the  suspension  bearings  of  tur- 
bines. The  Boyden  wheel  was  generally,  at  first,  provided 
with  a  suspension  box  at  the  top  of  the  shaft,  made  in  the 
above-described  manner,  and  a  guide-bearing  at  the  bottom  t 
Fig.  136.  This  method  has  latterly  fallen  into  disuse,  and 
most  vertical  shafts  of  turbines  now  run  on  wooden  step-bear- 
ings. This  arrangement  is  seen  in  the  Swain  turbine,  Figs. 
138  and  139,  and  in  the  Victor  turbine,  Fig.  147.  The  wooden 
block  rests  in  a  socket  which  is  usually  supported  by  cross-trees 
in  the  draft-tube,  but  sometimes  on  the  bottom  of  the  pit. 


STEP  AND   SUSPENSION  BEARING.  319 

Usually  the  bottom  of  the  shaft  is  squared  and  enters  a  broad 
foot  which  rests  on  the  wooden  block,  the  lower  surface  of  the 
foot  being  spherical  or  conical  and  bearing  on  the  ends  of  the 
fibres  of  the  block.  In  the  Risdon  turbine,  Fig.  144,  the  foot 
is  formed  on  the  shaft.  The  block  is  sometimes  free  to  revolve 
in  its  socket,  so  that  if  the  upper  surface  becomes  heated,  so 
as  to  greatly  increase  the  friction,  the  block  will  revolve  on  its 
lower  surface  and  give  the  upper  surface  time  to  cool.  The 
Geyelin  wheel,  Fig.  148,  runs  on  a  suspended  shaft.  When 
the  step-bearing  was  introduced,  it  was  thought  that  nothing 
but  lignum  vitae  or  some  of  the  very  heavy,  close-grained 
Southern  woods  would  answer  for  steps,  but  maple  and  oak 
are  found  to  work  very  well.  It  is  a  common  practice,  in  pre- 
paring steps,  to  dry  the  wood  thoroughly  and  then  •  boil  it  in 
linseed  oil,  impregnating  it  so  fully  that  it  becomes  in  .some 
measure  self-lubricating.  Such  steps,  although  constantly 
immersed  in  water,  sometimes  become  heated  so  as  to  char  the 
wood  and  soften  the  iron. 

Fig.  158  represents  a  form  of  step-bearing  patented  in  the 
United  States  by  the  writer  some  fifteen  years  ago  (in  about 
1885).  It  is  understood  that  bearings  on  this  principle  have 
recently  found  application  in  England.  The  shaft  rests  on  the 
revolving  plate  a,  which  in  turn  rests  on  the  stationary  block  b. 
The  shaft,  as  shown,  rests  on  a  in  such  a  manner  as  not  to 
interfere  with  the  free  distribution  of  the  weight  upon  b.  The 
surfaces  of  contact  between  a  and  b  are  dressed  to  an  exact  fit, 
and  the  wear  keeps  them  in  that  condition.  The  cylinder  g 
is  attached  to  b  and  provided  with  a  stuffing-box  embracing 
the  shaft.  Oil  for  lubrication  comes  through  the  pipe  <?,  being 
forced  in  under  great  pressure  by  a  small  pump.  It  fills  the 
space  f,  and  exerts  a  pressure  on  the  plate  a  nearly  but  not 
quite  equal  to  the  weight  of  the  shaft  and  its  attachments,  so 
that  the  contact-surfaces  sustain  very  moderate  friction.  The 
oil  passing  these  surfaces  fills  the  space  c  and  would  come  to 
great  pressure  there  if  confined.  The  pipe  d  communicates 
with  this  space  and  conveys  the  oil  back  to  the  tank  from  which 


320 


TURBINES. 


the  pump  draws  its  supply.  The  pressure  on  the  stuffing-box 
is  very  slight,  and  the  latter  need  not  be  screwed  tight  enough 
to  occasion  any  sensible  loss  of  power. 

In  the  turbines  recently  erected  at  Niagara  Falls,  the 
weight  of  the  wheel,  shaft,  and  attachments,  including  the 
armature  of  the  great  5OOO-h.p.  generator,  is  borne  without 
step  or  suspension  bearing.  To  understand  how  this  is  done, 
we  revert  to  Fig.  136,  which  is  a  section  of  the  Boyden  wheel. 
Suppose  the  shaft,  disk-pipe,  and  casing  to  be  continued  some 


FIG.  158. 

TO  feet  upward,  the  disk-pipe  to  terminate  in  a  second  disk,  and 
this  to  be  surmounted  by  a  second  wheel  attached  to  the  shaft, 
the  wheel  and  disk  being  inverted  and  the  shaft  continuing  up 
to  the  upper  level.  The  closed  chamber  formed  by  the  two 
disks  and  the  casing  is  supplied  by  a  pipe  entering  horizontally. 
It  will  be  perceived  in  Fig.  136  that  the  web  of  the  wheel  is 
perforated  with  openings,  while  the  disk  is  continuous ;  an 
arrangement  which  relieves  the  wheel  from  any  pressure  of 


THE  BRIDGE-TPEE.  $21 

water.  The  upper  wheel  and  disk  are  arranged  in  reverse 
order.  The  disk  is  perforated,  while  the  web  of  the  wheel  is 
continuous,  allowing  the  entire  pressure  of  the  head  to  act 
upward  against  the  weight  of  the  wheels  and  their  attachments. 

The  Bridge-tree. — A  wheel  running  on  a  vertical  shaft 
usually  sits  below,  or  not  much  above,  the  lower  level,  while 
the  power  usually  has  to  be  made  applicable  above  the  upper 
level.  This  necessitates  a  support  at  a  greater  or  less  height, 
not  only  for  the  upright  shaft,  but  for  the  horizontal  shaft  to 
which  it  gives  motion,  and  so  formed  as  not  to  interfere  with 
the  motion  of  the  gears  which  transmit  the  movement  from  one 
to  the  other.  This  support  is  called  the  bridge  tree.  On  a 
moderate  or  low  fall  the  bridge-tree  can  usually  rest  on  the 
flume;  but  a  high  fall  requires  such  a  support  at  a  considerable 
distance  above  the  flume.  A  very  neat  example  of  a  bridge- 
tree  resting  on  the  flume  is  show'n  in  Fig.  156.  It  is  in  two 
halves,  the  lower  of  which  is  bolted  to  a  flange  on  the  neck 
which  projects  from  the  iron  flume.  This  carries  a  guide-bear- 
ing for  the  upright  shaft.  The  upright  half  or  yoke  is  bolted 
to  the  lower  by  flanges  and  likewise  carries  a  guide-bearing  in 
addition  to  the  bearing  for  the  horizontal  shaft.  The  crown- 
gear  thus  works  in  the  recess  between  the  two  halves  of  the 
bridge-tree  and  is  very  firmly  supported  by  the  two  bearings. 

Fig.  159  shows  a  bridge-tree  in  the  form  of  a  heavy  casting 
resting  on  masonry  walls.  This  occurs  on  a  head  of  50  or  60 
feet,  which  brings  the  horizontal  shaft  at  a  considerable  height 
above  the  flume.  The  gears  are  proportioned  so  as  not  to 
change  the  relative  velocity  of  the  horizontal  and  vertical  shafts. 
This  design  is  given  by  the  Dayton  Globe  and  Iron  Works, 
Dayton,  Ohio. 

Fig.  1 60  shows  a  bridge-tree  designed  to  be  supported  upon 
rolled  I  beams.  The  beams  are  arranged  in  pairs,  and  the 
connection  is  made  by  means  of  cast-iron  brackets  bolted 
through  the  web  of  the  beam  where  a  bolt-hole  does  not  sensi- 
bly weaken  the  beam.  The  tree  carries  the  bearing  for  the 
vertical  and  also  for  the  horizontal  shaft,  these  bearings  being 


322 


TURBINES. 


FIG.  159. 


THE  BRIDGE-TREE. 


323 


FIG.  160. 


324 


TURBINES . 


to  some  slight  extent  adjustable  laterally.  It  will  be  noticed 
that  this  arrangement  contemplates  an  iron  gear  on  the  hori- 
zontal shaft,  and  a  wooden  mortise  gear  on  the  vertical.  Such 
a  pair  of  gears  runs  with  much  less  noise  and  is  less  liable  to 
breakage  than  a  pair  of  iron  gears.  This  design  is  given  by 
the  Dayton  Globe  Iron  Works  Company. 

Fig.  161  is  a  simpler  form  of  bridge-tree  designed  for  attach- 
ment to  a  wooden  beam,  and  suitable  for  a  low  head.     The 


FIG.  161. 

upright  shaft  here  has  two  bearings,  one  attached  to  the  beam, 
the  other  to  the  bridge-tree.  It  will  be  noticed  that  the  bridge- 
tree  is  adjustable,  as  well  as  the  bearings  which  are  attached  to 
it.  The  bolt-holes  through  the  foot  of  the  tree  are  somewhat 
elongated,  so  as  to  admit  of  a  slight  movement  of  the  tree  after 
the  bolts  are  inserted.  Before  turning  up  the  nuts  the  tree  is 
brought  into  the  right  position  by  the  wedges.  Similar  adjust- 
ments are  seen  on  the  bearings  attached  to  the  bridge-tree. 
This  design  is  borrowed  from  S.  Morgan  Smith. 

Disconnecting  Mechanism. — The  power  of  several  turbines 
is  often  transmitted  through  the  same  shaft,  either  by  bevel- 


DISCONNECTING   MECHANISM.  325 

gears,  when  they  run  on  vertical  shafts,  or  directly,  when  all  run 
on  the  same  horizontal  shaft.  The  same  shaft  may  also  have 
a  connection  with  the  steam-engine.  The  establishment  runs, 
at  times,  entirely  by  water ;  as  the  water  diminishes  in  the  dry 
season,  one  wheel  after  another  is  put  out  of  use,  and  in  the 
driest  weather  it  may  run  wholly  by  steam.  For  this  and 
other  reasons  it  is  often  desirable  to  throw  a  wheel  out  of  con- 
nection with  the  general  system. 

Fig.  162  shows  the  simplest  de- 
vice for  disconnecting  a  horizontal     

shaft.      It  consists    of  a  common 
face-coupling,  the  two  faces  stand-  FIG.  162. 

ing  about  an  inch  apart,  and  the  two  parts  of  the  shaft  which 
they  unite  being  separated  "by  the  same  distance.  To  connect 
the  shafts  we  insert  a  disk  of  inch  plank,  both  disk  and  faces 
being  bored  for  bolts.  These  are  passed  through  and  the  nuts 
turned  up.  A  double  bearing  is  required  at  the  point  of  discon- 
nection. This  device  is  of  limited  application.  In  a  series  of 
turbines  numbered  i,  2,  3,  4,  etc.,  all  transmitting  through 
the  same  shaft,  it  is  possible  by  this  means  to  cut  off  No.  i  or 
i  and  2,  or  i,  2,  and  3,  leaving  the  others  running;  but  it 
would  not  be  possible  to  cut  off  No.  2  and  leave  No.  i  running, 
etc. 

The  disconnecting-coupling  indicated  by  Fig.  163  has  been 
used  on  vertical  shafts.  By  turning  the  screw  we  lower-  the 
upper  part  of  the  shaft  and  draw  the  crown-gear  out  of  connec- 
tion. By  this  device,  any  wheel  gearing  into  a  horizontal  line 
of  shafting  may  be  cut  out  of  the  system. 

Figs.  164,  164^,  and  164^  show  a  disconnecting  device 
applicable  to  small  Shafts  for  which  a  patent  was  granted  to 
the  writer  from  the  United  States  under  date  of  April  27,  1897. 
Shafts  b  and  a  are  supposed  to  be  driven  by  separate  motors, 
and  it  may  be  required  to  throw  on  or  off  the  line  b  without 
stopping  the  line  a.  b  transmits  power  to  a  by  means  of  the 
spring-pawls  c  c.  When  b  is  thrown  off,  the  pawls  begin  to 
pound,  and  continue  to  do  so  till  b  comes  to  rest,  when  they 


326 


TURBINES. 


can  be  confined  out  of  contact  by  thrusting  small  wooden 
wedges  under  the  springs.  In  starting  the  wheel,  which  is 
geared  to  $,  these  wedges  are  removed,  when  the  noise  com- 


FIG.   1640. 


FIG.  164*$. 


mences  and  continues  till  the  pawls  come  to  a  bearing.  As 
the  speed  of  b  increases,  the  clicks  diminish  in  frequency,  and 
this  guides  the  workman  in  bringing  the  pawls  to  a  bearing 
without  shock.  In  fact  no  shock  can  occur,  for  as  soon  as  the 
Speed  of  b  becomes  equal  to  that  of  a  the  pawls  come  to  a 
bearing. 

The  Friction-clutch. — The  foregoing  devices  relate  to  the 
problem  of  connecting  or  disconnecting  two  shafts  while  they 
are  stopped,  or  of  starting  a  motor  to  join  one  already  running. 
To  put  in  motion  a  line  of  shafting  or  a  heavy  machine  by  a 


THE  FRICTION-CLUTCH. 


327 


line  already  running  requires  a  different  device,  viz.,  a  friction- 
clutch.  This  consists  of  a  disk,  pulley,  or  wheel  attached  to 
each  of  the  shafts,  combined  with  means  of  creating  such 
mutual  friction  between  them  as  to  cause  them  to  revolve'in 
unison. 

Fig.   165  shows  in  a  schematic  manner  the  principle  of  the 


FIG. 


friction-clutch.  It  is  more  intelligible  than  a  finished  cut  in 
which  the  principle  is  obscured  by  constructive  details.  5  is 
the  moving  shaft,  Sf  the  shaft  to  be  set  in  motion.  The  shaft 
S  carries  the  sleeve  A  attached  by  a  loose-fitting  spline  which 
causes  the  sleeve  to  revolve  with  the  shaft,  but  leaves  it  free  to 


328  TURBINES. 

move  longitudinally  thereon.  The  collar  B  runs  in  a  groove 
on  the  sleeve,  which  confines  it  laterally,  but  leaves  it  free  to 
remain  fixed  while  the  collar  revolves.  This  collar  carries  two 
gudgeons  which  are  seized  by  the  forked  lever  seen  at  Figs. 
165  and  1650.  To  the  shaft  S'  is  affixed  a  hub  carrying  a 
pulley  with  a  wide  rim  against  which  bear  the  friction-blocks 
CC.  These  latter  are  connected  with  the  sleeve  by  the  arms 
RR.  A  pull  upon  the  lever,  carrying  the  outer  end  to  the  left, 
advances  the  sleeve  and,  through  the  levers  RR  which  act  as 
a  toggle,  presses  the  frictjon-blocks  against  the  rim  of  the  pulley 
with  such  force  that  the  friction  exceeds  the  resistance  to 
motion  and  the  shaft  revolves.  The  arms  are  very  strong  and 
strongly  jointed  to  the  sleeve  to  bear  the  transverse  strain  of 
the  friction.  They  may  be  two,  four,  or  six  in  number.  The 
friction-blocks  are  elongated  segments  bearing  against  the  inner 
face  of  the  pulley,  and  are  formed  so  that  the  connections  have 
•a  slight  degree  of  elasticity.  .They  are  also  fitted  with  adjust- 
ments for  taking  up  the  wear.  In  the  position  of  Fig.  165,  if 
we  advance  the  sleeve  so  as  to  set  S'  in  motion,  and  clamp  the 
lever  in  that  position,  there  is  an  end-long  strain  on  the  shaft, 
requiring  a  thrust-bearing  and  occasioning  friction.  If,  how- 
ever, we  advance  the  sleeve  till  the  inner  ends  of  the  levers 
are  in  advance  of  the  outer  ends,  the  elastic  strain  on  the  levers 
holds  the  sleeve  against  the  face  of  the  pulley  Sf,  and  the 
device  is  locked,  causing  no  extra  friction  on  the  shaft-bearings. 

In  Fig.  1 66  the  rim  of  the  pulley  S'  is  gripped  by  two  fric- 
tion-blocks, C  on  the  inside,  D  on  the  outside.  The  advance 
of  the  sleeve,  acting  through  the  bent  lever,  draws  D  against 
the  outer  face  and  presses  C  against  the  inner  face.  In  this 
case  the  blocks  are  sustained  and  forced  to  revolve  by  connec- 
tions with  a  disk  on  the  sleeve,  the  nature  of  which  we  need 
not  enter  into. 

Fig.  167  shows  the  most  recent  arrangement  for  throwing 
in  and  out  a  belt,  shaft,  or  machine  by  means  of  a  friction  - 
coupling.  It  shows  a  shaft,  which  we  will  call  the  main  shaft, 
supported  in  bearings.  Rigidly  attached  to  this  shaft  is  the 


THE  FRICTION-CLUTCH. 


329 


FIG.  166. 


FIG.  167. 


330  TURBINES. 

disk  and  the  sliding  sleeve  of  the  friction-clutch.  This  is  close 
to  one  of  the  bearings  of  the  main  shaft.  The  remainder  of  the 
space  between  two  consecutive  bearings  is  occupied  by  a  hollow 
shaft  outside  the  main  shaft.  This  also  rests  in  bearings  and 
carries  the  pulley  or  gear  giving  motion  to  the  disconnectible 
shaft  or  machine.  It  also  carries  the  corresponding  half  of  the 
friction-clutch.  This  hollow  shaft  is  called  a  quill.  When 
not  in  motion  it  has  no  connection  with  the  main  shaft  and 
offers  no  impediment  to  its  motion.  When  the  clutch  is  thrown 
in  gear  by  means  of  the  handle,  Figs.  165  and  1650,  the  quill 
revolves  with  its  attachments. 

The  Penstock. — This  term  is  applied  to  the  pipe  which 
brings  the  water  from  the  canal  or  other  source  of  supply  to  the 
flume.  It  is  a  very  unimportant  detail  of  the  system  when  the 
source  of  supply  is  near  the  wheel.  When,  however,  as  some- 
times occurs,  it  takes  a  length  of  miles,  it  becomes  of  primary 
importance,  and  phenomena  are  developed  in  it  which  it  is  very 
necessary  to  understand. 

Such  pipes  are  commonly  made  of  riveted  wrought-iron  or 
steel  plates.  Modern  rolling-mills  produce  single  sheets  large 
enough  to  make'a  length  of  pipe  up  to  a  diameter  of  6  feet,  and 
probably  greater  if  required.  The  use  of  such  sheets  is  very 
advantageous  as  diminishing  the  amount  of  riveting,  which 
greatly  increases  the  resistance  to  the  flow  of  water.  The 
running  joints  are  formed  by  bending  the  sheet  into  the  form 
of  a  cylinder  and  riveting  the  edges  to  a  separate  plate  called 
a  butt-strap.  Sometimes  two  such  plates  are  used,  one  inside, 
the  other  outside.  The  circular  joints  are  formed  by  riveting 
each  length  to  a  ring  outside  the  pipe.  Necessarily  a  part  of 
this  latter  riveting  has  to  be  done  on  the  ground.  To  prevent 
corrosion  and  increase  the  durability  of  such  pipes,  they  are 
immersed  in  a  bath  of  coal-tar  thickened  with  asphaltum,  at  a 
temperature  of  about  300°  F. 

In  the  case  of  a  long  line,  nearly  level  but  impracticable 
for  a  canal,  large  pipe  made  of  wooden  staves  and  banded  with 
iron  hoops  has  been  successfully  used.  This  pipe  is  not  made 


THE  PENSTOCK. 


331 


in  uniform  lengths  and  then  put  together,  but  built  as  a  contin- 
uous structure,  the  staves  breaking  joints  with  each  other.     Fig. 


FIG.  168. 


FIG.  169. 
is  a  cross-section,  Fig.  169  an  elevation,   of  such  a  pipe 


1 68 

6  feet  diameter. 


It  is  composed  of  staves  about  8  inches  wide, 


332  •  TURBINES. 

made  of  2^-inch  plank,  and  12  to  20  feet  in  length.  The 
bands  are  composed  off-  or  f-inch  round  iron,  two  rods  being- 
required  for  a  complete  band.  The  upper  one  is  formed  with 
a  loop  at  each  end,  which  embraces  a  wooden  or  iron  block 
called  a  shoe.  The  lower  half  of  the  pipe  is  encircled  with  a 
rod  having  a  screw-thread  at  each  end.  These  pass  through 
the  blocks  and  are  secured  by  nuts,  by  which  any  desired  strain 
can  be  brought  upon  the  hoops.  The  pipe  rests  in  cradles  of 
6"  X  8"  or  8"  X  8"  timbers  spiked  or  drift-bolted  together, 
of  a  length  somewhat  greater  than  the  diameter  of  the  pipe,  and 
at  distances  apart  about  equal  to  their  length.  In  order  to 
break  joints  the  staves  must  be  of  exactly  uniform  width.  The 
tightness  of  the  running  joints  is  secured  by  the  strain  on  the 
hoops.  The  abutting  end-joints  have  a  saw-cut  £  or  f  inch 
deep  for  the  insertion  of  an  iron  tongue  whose  length  is  a  little 
greater  than  the  width  of  the  stave  and  which  is  forced  to  a 
slight  extent  into  the  adjoining  staves. 

Such  a  pipe  can  receive  a  considerable  curvature  either 
horizontal  or  vertical.  To  effect  this  the  part  under  construc- 
tion is  put  together  and  lightly  banded  so  as  to  hold  it  in  shape 
but  not  prevent  a  slight  relative  movement  of  the  staves.  It 
is  then  forced  out  of  line  by  weights,  by  block  and  tackle,  or 
by  a  screw-jack.  When  it  has  the  desired  curvature  the  bands 
are  all  put  on  and  the  nuts  turned  up  tight.  In  this  condition 
it  will  not  return  to  its  original  form.  If  it  is  slightly  deformed 
in  the  process  of  bending,  the  tightening  of  the  bands  tends  to 
restore  the  circular  form. 

A  long  penstock  presents  peculiar  difficulties  as  regards  the 
regulation  of  the  flow  of  water  to  correspond  with  the  require- 
ments of  the  power.  In  a  6-foot  penstock  a  mile  long,  the 
water  in  motion  has  a  weight  of  more  than  4000  tons.  Any 
material  diminution  of  velocity  in  such  a  pipe  implies  the  sudden 
slowing  up  of  this  enormous  mass,  and  cannot  fail  to  exert 
great  pressure  upon  the  pipe.  We  will  endeavor  to  obtain 
some  idea  of  the  effect  of  changes  of  velocity  in  such  a  pipe. 

Assume  a  long  pipe  filled  with  water,  Fig.   170.      Imagine 


THE  PENSTOCK.  333 

at  A£  a.  piston  to  start  forward,  and  suppose  that  when  it  has 
moved  the  distance  /  it  has  set  the  water  in  motion  as  far  as 
CD. 


FIG.  170. 

Let  r  =  radius  of  pipe  in  feet ; 

w  =  weight  of  one  cubic  foot  of  water ; 

m  =  modulus  of  elasticity  of  water,  say  294000  X   T44 

pounds  per  square  foot; 
M  =  modulus  of  elasticity  of  metal  of  pipe,  pounds  per 

square  foot ; 

T=  thickness  of  pipe,  feet; 
/  =  time  occupied  by  the  piston  in  moving  the  distance 

/  in  seconds ; 

v  =  velocity  of  piston  in  feet  per  second ; 
/"=  force   exerted   upon  the    water  by  the   piston   in 

pounds  per  square  foot; 
L  =  the   distance  from   the  piston  to  the  particles  of 

water   that  are  in  the  act  of  commencing  to 

move  when  the  piston  has  moved  a  distance  / 

in  feet. 

When  the  piston  has  moved  a  distance  /,  although  it  has 
only  moved  the  centre  of  gravity  of  the  mass  L  a  distance  £/, 
it  has  done  work  in  compressing  the  watef  and  distending  the 
pipe  equivalent  to  moving  the  mass  a  distance  /  and  imparting 

to  it  the  velocity  - .      This  will  appear  on  reflecting  that  if  the 

forces  opposing  the  movement  of  the  mass  were  suddenly 
removed,  the  latter  would,  by  release  of  pressure,  acquire  the 
velocity  stated. 

The  bursting  tension  on  a  running  foot  of  the  pipe  is  rf. 


334  TURBINES. 

r2/ 
The  increase  in  the  radius  is  TJ-      Increase  in  cross-section 


m 

=  27tr-TT^  =  271-—^.      Increase  of  volume  =  //27r-v™. 
Ml  Ml  JJ  J 

Traverse  of  piston  due  to  distension  of  pipe  =  L-^j,. 

"         «        "        "    "  compression  of  water  =  L  -r. 

r    (  2r         i  \  2rm-\-MT 

•  Total  traverse  of  piston  =  Lf  (j^  -f  —)=£</     mMf~  =  /- 

Velocity  of  piston  in  feet  per  second  =  v  =  - 
Lf2rm  +  MT 

~-~~~~'      •    -    •    •    (47) 


The  total  weight  of  water  set  in  motion  is  n 

The  force  acting  to  impart  motion  is  7rr*f. 

Gravity,  acting  freely,  would  impart  to  the  mass  a  velocity 
of  gt  feet  per  second  in  the  time  /,  whence  we  have  the  pro- 
portion 

-  :  gt  =  Ttr2/  :  nr*Lw} 


whence 
L      gt*f    f 

mMT 

•    L-^ 

mMT 

~    hv  '     / 

L(2rm  -\-MTj 

(2rm  +  M 

Whence  we  find  =  -  

/        V    «'  2rm  +  MT 

Taking  M  =  30  ooo  ooo  X  144,  m  as  above,  T  =  \  inch 
=  T1^  foot,  and  r  =  2.5  feet,  we  find—  =  V  =  velocity  of" 

pulsation  =  2551  feet  per  second. 

So  that,  if  we  conceive  of  a  pipe-line  such  as  here  contem- 
plated reaching  from  Boston  to  Chicago,  something  over  half 
an  hour  must  elapse  after  the  starting  of  the  pumps  at  Boston 
before  the  water  would  commence  to  flow  at  Chicago.  This 
would  be  true  whether  the  pumps  worked  fast  or  slow.  The 


THE  PENSTOCK.  335 

entire  pumpage  of  the  interim  would  be  absorbed  by  the  dis- 
tension of  the  pipe  and  the  compression  of  the  water. 
Eq.  (48)  may  be  put  under  the  form 

L  _         /  g        m 
t      \        w  2rm    ' 


The  assumption  that  there  is  no  distension  of  the  pipe  implies 
an  infinite  value  of  M,  which  would  make 

—  =  A  /  m—  =  4672  feet  per  second,      .      .     (49) 

t  y          W 

being  substantially  the  velocity  of  sound  in  water,  which  is 
usually  taken  at  about  4700  feet  per  second. 

Instead  of  a  piston  suddenly  starting  forward,  imagine  water 
moving  with  the  velocity  v,  to  be  suddenly  arrested  by  the 
closing  of  a  gate,  f  is  then  the  force  acting  against  the  gate 
and  walls  of  the  pipe.  To  find  the  value  of  f,  we  reason  as 
follows : 

If  O  be  the  volume  of  a  mass  of  water  under  atmospheric 
pressure,  and  Ol  its  volume  under  the  pressure/",  then 

0-0, 


Let  Ll  be  the  value  of  L  when  t  =  i.  Then  the  volume  of  the 
mass  of  water  that  we  are  considering,  under  atmospheric 
pressure,  is 

7rr2(Z1  -{-  z').      Do.  underpressure/,  ir**L^l  -f- 
whence 


/=* ZTT^"  •   '   '   (50) 

If  we  make  M  infinite  in  this  equation,  it  reduces  to 

/=  -* 


336  TURBINES. 

which  for  v  =  4  feet  would  give  f  =  ->—  ^  =  2  5  1  .  5  pounds  per 

4070 

square  inch.      Equation  (50)  takes  the  form 
(L,  +  *y=  m  {  L-  +  v  - 

or      MT(L^  +  ?')/  -  »<A  +  "i'WT  -  mLMT  -  2rmLj, 
whence 

_  ;;/(£,  +  ^1/r  -  mL.MT  _  •_  _  mi'MT  _ 

'       -  ~  ( 


Taking  v  =  4  and  other  symbols  as  before,  we  find  f  —  75 
pounds  per  square  inch. 

As  i'  is  always  very  small  compared  with  Ll  ,  it  will  be  seen 
that  the  pressure  is  sensibly  proportional  to  the  velocity 
destroyed. 

The  above  equations  indicate  that  /  is  theoretically  in- 
dependent of  the  length  of  the  pipe,  but  this  can  only  be  true 
on  the  assumption  that  the  stoppage  is  absolutely  instantaneous. 
Under  practical  conditions,  in  which  the  stoppage  occupies  an 
appreciable  time,  the  force  developed  is  not  independent  of  the 
length.  For  the  purpose  of  experiment  a  valve  may  be  used 
causing  an  instantaneous  stoppage,  though  such  valves  are 
ordinarily  avoided,  and  upon  the  closure  of  such  a  valve  the 
full  pressure  is  instantly  developed  on  it.  The  section  in  which 
the  water  is  coming  to  rest  moves  up-stream  with  the  velocity 
indicated  by  equation  (49).  The  amplitude  of  this  movement 
is  only  limited  by  the  length  of  the  pipe,  above  the  valve, 
either  to  the  reservoir  or  to  the  larger  pipe  or  canal  from  which 
it  branches. 

Neglecting  the  elasticity  of  the  pipe,  the  time  occupied  by 

j^- 
its  contents  in  coming  to  rest  is  —  ^  —  =  /,  X  being  the  total 

length.      The  water  has  continued  to  flow  into  the  pipe  with 


THE  PENSTOCK.  337 

the  undiminished   velocity  v,   for   /  seconds  after  the  closure. 
The  compression  of  the  water  in  the  pipe  is  represented  by  Ap, 


and  the  force  exerted  on  the  interior  by  m-^.  =  MJ-  pounds 

A          Ll 

per  square  inch,  m  being  the  modulus  per  square  inch.  A  pipe 
buried  and  firmly  packed  in  the  ground,  as  is  the  ordinary 
practice  with  penstocks,  is  probably  in  a  condition  to  require 
the  elasticity  to  be  neglected  in  computing  the  pressure,  and 
such  a  pipe  might  have  parts  not  so  protected  on  which  the 
pressure  would  be  liable  to  act  dangerously. 

The  pressure  on  a  suddenly  closed  valve  is  not  released 
when  the  entire  contents  of  the  pipe  have  come  to  rest.  The 
water  at  that  instant  is  in  a  state  of  compression  throughout  the 
entire  length  X  of  the  pipe.  A  release  and  reversal  of  motion 
takes  place  commencing  at  the  origin  of  the  pipe,  and  moves 
toward  the  valve  with  the  velocity  V  =  Ll  feet  per  second,  so 
that  the  time  from  the  stoppage  to  the  release  of  pressure  is  2t. 
A  series  of  blows  or  shocks  on  the  valve  will  recur  at  intervals 
of  2t  till  the  movement  dies  out.  This  is  always  observed  in 
service-pipes  when  the  abrupt  closing  of  a  valve  is  followed  by 
a  harsh  grating  sound.  In  a  service-pipe  100  feet  long, 
neglecting  elasticity,  these  blows  would  occur  at  the  rate  of 
about  twenty-three  per  second. 

In  confirmation  of  these  views  the  following  may  be  quoted 
from  the  Engineer  (London)  in  reference  to  the  power-house 
at  Fresno,  Cal.,  which  is  supplied  by  a  pipe  4000  feet  long 
under  a  head  of  1400  feet,  some  600  pounds  per  square  inch: 
"The  gates  are  controlled  at  the  power-house  by  hydraulic 
rams.  In  opening  the  gates  as  at  first  designed  a  fluctuation 
of  170  pounds  above  and  below  the  normal  was  brought  about. 
That  is  to  say:  the  pressure  would  first  drop  to  90  pounds 
below  normal,  then  rise  to  180  pounds  above,  then  sink  to  75 
pounds  below  normal,  and  continue  '  diminuendo  '  until  the 
normal  pressure  was  reached.  A  similar  phenomenon,  but 
reversed  in  order,  occurred  when  the  gates  were  closed,"  etc. 


338  TURBINES, 

When  a  valve  occupies  an  appreciable  time  in  closing  it  is 
easy  to  understand  that  the  resulting  pressure  will  depend  upon 
the  length  of  the  pipe.  The  closing  may  be  supposed  to  take 
place  by  a  great  number  of  small  steps  each  of  which  may  be 
regarded  as  instantaneous.  Each  step  occasions  a  certain 
diminution  of  velocity  and  is  accompanied  by  an  increment  of 
pressure.  Each  increment  runs  to  the  head  of  the  pipe,  and 
the  release  returns  with  the  same  velocity.  Every  increment 
of  pressure  originating  at  the  valve  remains  in  force  there  till 
the  pulsation  has  run  to  the  head  of  the  pipe  and  back  to  the 
valve.  Therefore,  whatever  diminution  of  velocity  may  be 
effected  during  the  interval  2/  may,  for  purposes  of  computa- 
tion, be  regarded  as  instantaneous.  This  is  true  for  any  point 
of  the  pipe  when  we  use  the  value  of  /  corresponding  to  that 
point. 

The  important  point  in  this  inquiry  is  to  determine  the 
pressure  generated  in  the  ordinary  operation  of  regulating  the 
power.  Consider  a  penstock  in  which  the  elasticity  of  the 
metal  can  be  disregarded,  and  long  enough  so  that  2/  seconds 
will  suffice  for  any  required  change  in  the  power.  Let  v  = 
the  normal  velocity  of  the  water,  and  P  =  the  normal  pressure 
in  the  pipe.  Suppose  the  demand  for  power  to  suddenly 
diminish  one-fourth,  and  the  power  to  automatically  adjust  itself 
to  this  requirement  within  the  time  2/.  Let/^  be  the  pressure, 
and  ?'j  the  velocity,  at  the  instant  this  adjustment  is  effected. 
We  must  have 


'i 
From  these  two  equations  there  will  result 


whence 


REG  ULA  TION.  3  39 

Taking  the  values  of  P  and  v  as  contemplated  in  the  Pioneer 
Electric  Plant*  at  Ogden,  Utah,  viz.,  P  =  216.67,  v  =  9,  we 
find  Pl  =  638.96,  which  is  the  momentary  pressure  that  the 
pipe  would  be  subjected  to  in  the  case  supposed  if  the  velocity 
could  be  controlled  in  precise  accordance  with  the  requirements 
of  the  power. 

We  might  make  eq.  (52)  entirely  general  by  putting  a  for 
the  fraction  that  the  reduced  power  is  of  the  normal  power. 
Then  we  should  have 


P  +      _  aP.    (53) 

Regulation. — Industrial  operations  require  a  uniform  speed 
of  shafting,  although  the  quantity  of  work  or  the  number  of 
machines  in  operation  may  vary  greatly  from  hour  to  hour  or 
even  from  minute  to  minute.  This  condition  necessitates  an 
automatic  device  for  controlling  the  admission  of  water  to  the 
wheel,  diminishing  the  same  where  the  velocity  exceeds  the 
normal  rate  and  vice  versa.  The  essential  part  of  this  device 
is  an  organ  which  moves  in  one  direction  and  sets  in  motion 
the  mechanism  for  closing  the  gate  when  the  velocity  exceeds 
the  normal  limit,  and  which  moves  in  the  opposite  direction 
and  sets  in  motion  the  mechanism  for  opening  the  gate  when 
the  velocity  falls  below  that  limit.  Such  a  movement  can  only 
be  secured  through  the  agency  of  centrifugal  force. 

Many  combinations  may  be  imagined  by  which  a  revolving 
weight  may  be  made  to  depart  from  its  axis  of  rotation  by  the 
action  of  centrifugal  force,  and  return  by  the  action  of  a  weight 
or  spring;  but  after  the  most  exhaustive  study  of  the  subject 
we  should  revert  to  the  arrangement  suggested  by  Fig.  171. 
A  heavy  weight  Wis  carried  by  an  arm  which  is  pivoted  to  a 
vertical  revolving  spindle  so  as  to  be  susceptible  of  a  swinging 
movement  in  the  plane  of  the  picture.  The  arm  and  ball 
rotate  around  the  spindle,  and  the  centrifugal  force  causes  the 

*  Trans.  Am.  Soc.  C.  E.,  vol.  xxxvill.  p.  246. 


340  TURBINES, 

arm  to  deviate  from  the  vertical.  For  every  velocity  of  rota- 
tion there  is  a  corresponding  angle  of  deviation  which  does  not 
change  while  the  velocity  remains  constant.  This  deviation 
of  the  arm  and  ball  from  the  vertical  constitutes  the  movement 
desired  for  the  regulator.  It  increases  or  diminishes  with  the 
velocity,  and  by  means  of  suitable  linkages  and  connections 
can  be  transferred  to  any  desired  part  of  the  mechanism. 

Let  GO  represent  the  angular  velocity  of  the  spindle,  Fig. 

171; 

/  =  the  length  of  the  arm  from  the  centre  of  suspension 
to  the  centre  of  the  ball  or,  if  great  accuracy  is 
aimed  at,  the  centre  of  gravity  of  arm  and  ball ; 
a  =  angle  of  deviation ; 
W  =  weight  of  ball,  or  of  ball  and  arm. 
The  force  tending  to  turn  the  ball  around  A  to  the  right  is 

W 

— G>?1  sin  a.     The  force  tending  to  turn  it  in  the  opposite  direc^ 

o 

tion  is  W.     Whence,  by  the  law  of  moments, 


W  , 

— ft?2/  sin  a  .  I  cos  a  =  Wl  sin  a, 

o 


whence 


—/cos  a  =  I, (54) 

o 
cr 

whence  cos  a  =  -j—y  from  which  it  appears  that  the  angle  of 

deviation  does  not  depend  at  all  upon  the  weight  of  the  balls, 
but  solely  upon  the  velocity  of  rotation. 

There  is  an  apparent  limitation  to  the  application  of  equa- 

<r 

tion    (54).      In   the  form   cos    a  =  ~^,   cos  a  cannot   exceed 

cr 

unity,  while  y-^  can  have  any  value  from  o  to  infinity.      The 


value  of  GO  from   (54)  is  &?  =  \  /  — - — .      This  equation 

y   /  cos  a 


REG  ULA  T1ON.  34 1 

give  no  value  of  GO  less  than  A/C-     For  the  arrangement  of 


Fig.   1 7 1  it  would  appear  that  values  of  GO  less  than  A  /C  must 


be  excluded.      This  difficulty,  however,  has  no  practical  con- 


FIG.   171. 

cern  for  us,  since  in  practice  the  pivot  of  the  arm  never  coin- 
cides with  the  axis  of  the  spindle.  The  arrangement  ordinarily 
adopted  is  that  of  Fig.  172,  in  which  the  arm  is  pivoted  to  a 
cross-bar  fastened  to  the  spindle.  Let  m  represent  the  distance 
of  the  point  of  suspension  from  the  axis  of  rotation.  In  this 
case 


W 

— -Goz(m  -f-  /  sin  a-)/  cos  a  =  Wl  sin  a, 

<5 


whence 


g  tan  a 

m  -f-  /  sin  a 


•     •     (55) 


In  this  equation,  which  appears  to  be  free  from  ambiguity, 
it  is  not  easy  to  assign  a  value  to  GO  and  compute  the  corre- 
sponding value  of  a,  but  it  is  easy  to  assign  a  value  to  a  and 
find  the  corresponding  value  of  GO.  GO  represents  the  velocity 

60  &7 
of  a  point  at  units  distance  from  the  axis  of  rotation,  and 


342  TURBIXES. 

=  the  number  of  revolutions  per  minute.  Making  in  equation 
(55)  /=  2  and  m  =  o.2$,  we  find  that  to  give  the  balls  a 
deviation  from  the  vertical  of 

10  degrees  requires  a  speed  of  29.44  turns  per  minute. 

15  "  "  »  "32.01  "  '•  " 

20  "  "  "  "  33-82  " 

25  "  ;<V:'  "  "  35-36  "  "  " 

30  "  -"  '  "  "  36.80  "  "  " 

35  ..  -  -  "38-36  "  "  " 

40  "  "  "  40.05  "  "  " 

45  "  '«  "  "  42.00  "  "  " 

50  "  "  "  "44-31  " 

55  ««  •«  "  -47.12  "  »  " 

60  »  "  "  "  50.65  "  «•  " 

65  "  "  "  "  55.25  «•  "  «« 

70  "  "  "  "61.55  "  "  " 

It  will  be  noticed  that  as  the  rotation  becomes  more  rapid 
it  requires  a  greater  increment  of  velocity  to  effect  a  given  in- 


FlG.   173.  FIG.   I73a. 

crement  in  the  deviation  of  the  balls.  The  regulator  is  more 
sensitive  to  a  change  of  speed  at  a  low  velocity  than  at  a  high 
one.  For  this  reason  it  is  not  customary  to  give  the  spindle  a 
speed  of  more  than  35  to  45.  turns  per  minute. 

Fig.  174  shows  an  old  form  of  regulator,  Y  being  the 
revolving  spindle  and  balls.  The  latter  are  connected  with 
the  collar  C,  which  revolves  with  the  spindle  but  is  susceptible 
of  a  slight  up-and-down  movement.  The  two  bevel-gears  A 
and  B  are  loose  on  the  spindle  and  mesh  with  the  larger  bevel- 
gear  on  the  shaft  D.  The  connection  of  the  arms  with  the 


REG  ULA  TION. 


343 


collar  C  is  shown  at  Figs.  173  and  1730.  Two  thin  splines 
run  in  grooves  cut  in  the  sides  of  the  spindle  and  are  attached 
to  the  collar  C,  The  arm  forms  an  elbow  at  the  suspension 
joint,  and  terminates  in  a  finger  which  seizes  a  projection  on 
the  spline,  raising  the  collar  C  when  the  balls  fall  and  lowering 


FIG.  174. 

it  when  they  rise.  The  collar  carries  a  projecting  stud  on  its 
upper  and  another  on  its  lower  face,  and  a  corresponding  stud 
is  borne  by  each  of  the  bevel-gears  A  and  B.  When  the 
velocity  is  normal,  these  studs  clear  each  other;  but  when  the 
velocity  diminishes,  the  balls  fall,  the  collar  rises  and  its  stud 
engages  with  the  upper  bevel-gear,  setting  it  in  motion  and 
turning  the  shaft  D  to  open  the  gate.  When  the  velocity  rises 
above  the  normal  limit,  the  contrary  action  takes  place  and 


344 


TURBINES. 


closes  the  gate.  The  shaft  D  carries  a  worm-gear  which  acts 
on  the  wheel  X,  and,  through  the  toothed  pinion  W,  on  the 
toothed  gate-stem  V.  The  spindle  is  revolved  through  the 
lower  bevel-gear,  G,  by  a  small  line  of  shafting  branching, 
at  any  convenient  point,  from  the  main  shafting.  The  shaft  D 
carries  a  friction-coupling,  which  insures  the  mechanism  against 


FIG.   175. 

breakage  when  the  gate  reaches  the  end  of  its  traverse.  The 
regulator  continues  in  action  after  the  gate  has  reached  its 
upper  limit,  and  if  the  mechanism  were  rigid  it  would  inevitably 
break.  When  the  wheel  is  coupled  to  others,  or  several  wheels 
are  geared  to  the  same  line  of  shafting,  the  regulator  may  con- 
tinue to  act  after  the  gate  has  reached  its  lower  limit.  Z  is  a 
rod  reaching  to  the  floor  above  and  carrying  a  hand-wheel  by 


REG  ULA  TION.  345 

which  the  gate  can  be  raised  and  lowered  by  hand ;  but  before 
turning  the  hand-wheel,  the  workman  places  his  foot  on  the 
head  of  the  rod  E,  and  operates  a  disconnecting-coupling  which 
frees  the  gate  from  the  action  of  the  regulator. 

Fig.  175  is  a  schematic  representation  of  a  governor  which 
has  received  extended  application.  The  upright  spindle,  which 
is  hollow,  receives  motion  from  the  shaft  A  driven  by  a  belt 
and  pulley.  Within  the  hollow  spindle  is  a  rod  firmly  attached 
to  the  double  friction-cone  D.  Two  hollow  friction-cones,  G 
and  H,  stand  one  above  and  one  below  D.  Connected  with 
these  hollow  cones  and  forming  a  part  of  them  are  bevel-gears, 
which  mesh  with  the  large  dish-shaped  bevel-gear  on  the 
shaft  B.  At  normal  speed  the  double  cone  runs  clear  of  both 
hollow  cones ;  but  a  slight  increase  of  speed  forces  it  into  the 
lower  cone  and  turns  the  shaft  B,  to  lower  the  gate,  and  vice 
versa.  The  disconnecting  mechanism  is  not  shown.  In  this 
form  of  regulator  the  cone  will  revolve  against  the  friction, 
when  the  gate  reaches  the  end  of  its  traverse,  before  any 
breakage  can  occur,  but  it  is  usual  to  introduce  a  friction-con- 
nection at  some  other  point  in  the  machine. 

Fig.  176  represents  the  leading  element  in  the  more 
modern  mechanism  of  the  regulator.  It  is  shown  as  applied 
to  the  cylindrical  gate  of  a  turbine  wheel,  by  means  of  three 
stems  A  A  A.  The  regulator  of  Fig.  174  acts  only  on  one  stem, 
and  would  not  work  to  raise  a  cylindrical  gate  unless  the  latter 
were  accurately  balanced  by  counterweights.  The  ring  F, 
Fig.  176,  is  toothed  on  the  outside  and  has  a  screw-thread  on 
the  inside,  which  acts,  when  the  ring  revolves,  to  raise  the  gate 
by  means  of  toothed  racks  on  the  stems  A  A  A.  S  is  the  shaft 
of  the  wheel.  An  arm  B  attached  to  a  ring  on  the  shaft  carries 
the  spring-pawls  DD,  and  has  a  constant  oscillatory  motion  of  a 
few  inches  to  right  and  left.  A  second  arm,  C,  carries  a  shield 
C;  which  masks  the  teeth  of  the  wheel  from  the  action  of  the 
pawls.  At  normal  speed  the  traverse  of  the  pawls  does  not 
carry  them  beyond  the  limits  of  the  shield,  and  the  regulator 
does  not  act.  The  revolving  balls  act,  through  suitable  linkages 


34°"  TURBINES. 

and  rods,  upon  the  arm  C,  and,  as  the  velocity  varies,  draw 
the  shield  aside  and  allow  the  pawls  to  act  on  the  teeth. 
When,  for  instance,  the  speed  falls  below  the  normal,  the  shield 
is  drawn,  say,  to  the  right,  and  the  left  pawl  acts  to  raise  the 
gate,  and  vice  versa.  If  the  change  of  speed  is  great,  the 
movement  of  the  shield  is  great,  and  the  ring  receives  a  large 


FIG.  176. 

movement  at  each  stroke  of  the  pawls.  If  the  change  is  slight, 
the  movement  imparted  to  the  gate  is  slight,  etc.  In  addition 
to  the  advantage  of  adapting  the  rapidity  of  its  action  to  the 
rapidity  in  the  change  of  velocity,  this  mechanism  may  be 
readily  thrown  out  of  connection  with  the  wheel  when  the  gate 
reaches  its  limit.  A  wheel  running  under  control  of  a  regulator 
often  runs  near  the  limit  of  its  capacity,  and  in  that  case  a  fric- 
tion-coupling is  liable  to  be  constantly  in  action  and  to  become 
dangerously  heated.  A  device  for  throwing  the  regulator 
wholly  out  of  gear  when  the  gate  reaches  its  limit  does  not 
meet  the  case.  It  must  be  thrown  out  of  gear  with  reference 


REG  ULA  TION.  347 

to  one  movement  of  the  gate,  and  remain  in  gear  with  reference 
to  the  contrary  movement;  otherwise  it  ceases  to  act  as  soon 
as  the  gate  reaches  its  limit.  Such  a  device  would  be  complex 
when  applied  to  the  mechanism  of  Figs.  174  and  175,  but  is 
very  simple  in  its  application  to  Fig.  176.  It  is  only  necessary 
to  arrange  so  that  when  the  gate  reaches  its  upper  limit  it  shall 
throw  the  left  pawl  out  of  action,  having  the  right  ready  to  act 
as  soon  as  the  velocity  increases.  The  left  comes  into  action 
as  soon  as  the  gate  lowers. 


CHAPTER   XVI. 

CANALS. 

A  FALL  available  for  water-power,  whether  created  by  a. 
dam  or  resulting  from  the  natural  conformation  of  the  ground, 
very  rarely  occurs  in  one  perpendicular  plunge.  The  more 
common  case  is  a  series  of  rapids  below  the  dam  or  waterfall, 
necessitating  a  more  or  less  extended  canal  in  order  to  utilize 
the  entire  fall.  Even  when  the  entire  fall  occurs  in  one  jump, 
a  canal  is  commonly  necessary  to  convey  and  distribute  the 
water  to  the  several  wheels. 

A  canal  in  earth  where  the  value  of  land  is  not  a  serious 
consideration  is  usually  made  with  sloping  sides.  The  slopes 
should  be  flatter  than  is  admissible  in  dry  embankments.  The 
canal  should  admit  of  being  frequently  and  rapidly  emptied, 
and  an  abrupt  lowering  of  the  water  tends  strongly  to  the 
caving  of  the  banks.  For  this  reason  it  is  not  advisable  to 
make  the  slopes  steeper  than  2  to  I.  In  populous  districts, 
where  land  is  of  high  value,  it  is  often  advisable  upon  economical 
and  sometimes  upon  aesthetic  grounds  to  flank  the  canal  with 
vertical  walls  of  masonry.  Fig.  177  indicates  a  canal  12  feet 
deep  with  slopes  of  2  to  I ,  the  water-surface  being  3  feet  below 
the  ground-level.  In  this  case  a  wall  placed  so  as  not  to 
change  the  cross-section  of  the  canal  would  save  about  18 
square  feet  of  ground  per  linear  foot  on  each  side  the  canal. 
A  linear  yard  of  this  wall  would  contain  about  7!  cubic  yards 
of  masonry,  and  it  would  make  available  for  other  uses  some 
54  square  feet  of  ground.  The  excavation  would  be  greater 
in  the  case  of  the  wall  than  in  that  of  the  slope.  Allowing 

348 


W ALLS. 


349 


3  dollars  a  cubic  yard  for  the  cost  of  the  masonry,  the  land  must 
be  worth  near  50  cents  a  square  foot  to  justify  the  wall.  Such 
walls  are  commonly  laid  without  mortar,  of  quarried  stone  such 
as  remain  after  the  dimension  stone  have  been  culled  out. 


FIG.  177. 

The  thickness  of  such  a  wall  should  be  at  the  bottom  about 
two-fifths  of  the  height,  and  about  one-fifth  at  the  top.  It 
must,  for  the  reason  above  given,  be  rather  heavier  than  for  a 
dry  embankment  of  the  same  height.  It  should  have  extra 
strength  when,  as  sometimes  happens,  a  railroad  runs  along 
the  bank  of  the  canal,  as  the  vibrations  incident  to  the  passage 
of  trains  and  locomotives  are  very  trying  to  such  work.  In 
such  case  the  bottom  width  should  be  one-half  the  height. 

When  a  canal  is  excavated  in  solid  rock  the  modern 
channelling-machine  may  be  used  with  great  advantage.  This 
is  an  automobile  engine  running  on  a  track  and  carrying  a  wide 
flat  tool  working  by  percussion  like  a  steam-drill,  but  capable 
of  cutting  a  continuous  channel  some  3  inches  wide  and  10  feet 
or  more  in  depth.  This  channel  greatly  facilitates  the  excava- 
tion of  the  rock  and  leaves  a  smooth  vertical  wall  for  the 
boundary  of  the  canal,  very  favorable  to  the  movement  of  the 
water.  When  the  rock  is  excavated  to  the  full  depth  of  the 
channel,  a  second  channel  can  be  cut  to  an  equal  depth,  leav- 
ing a  horizontal  offset  of  some  6  inches  in  the  face  of  the  wall. 
The  machine  can  run  on  a  curved  track,  to  conform  to  the  line 
of  the  canal,  when  required. 


35°  CANALS. 

The  Velocity  in  Canals  is  governed  by  two  considerations, 
viz. :  (i)  the  preservation  of  the  bed  and  banks  of  the  canal; 
(2)  the  preservation  of  the  head.  In  a  canal  with  side  slope? 
the  first  consideration  would  limit  the  velocity  to  from  I  foot 
in  sand  and  other  material  readily  disturbed,  to  3  feet  in  gravei 
interspersed  with  pebbles  the  size  of  an  egg.  In  a  formation 
of  pure  sand  or  pure  clay  a  velocity  of  less  than  I  foot  per 
second  will  affect  the  bed.  A  mean  velocity  of  4  inches  per 
second  would  act  perceptibly  upon  a  bed  of  fine  clay,  6  inches 
upon  fine  sand,  and  9  inches  upon  buckshot.  A  canal  in  a 
formation  of  these  materials  should  be  protected  by  some  arti- 
ikial  means.  Angular  broken  granite  of  the  size  used  for  road- 
croverings  is  not  easily  displaced  and  will  endure  a  velocity  of 
5  feet  per  second,  meaning  thereby  the  mean  velocity  in  the 
canal.  This  material  is  objectionable  as  forming  a  very  rough 
surface  and  offering  great  obstruction  to  the  flow  of  the  stream. 
Coarse  gravel  with  numerous  pebbles,  boulders,  and  cobbles 
soon  comes  to  a  permanent  condition  under  any  velocity 
attainable  in  a  canal.  The  sand  and  clay  js  washed  out,  leaving 
the  stones.  The  small  stones  fall  into  the  cavities  between  the 
large  ones  and  are  not  readily  detached.  In  a  walled  canal 
•with  its  bed  in  a  refractory  stratum  almost  any  desired  velocity 
can  be  used,  the  limiting  consideration  being  the  expense  of 
removing  the  great  quantities  of  silt  and  sediment  brought  in 
by  an  excessive  velocity.  As  to  the  second  consideration,  it 
is  a  balancing  of  the  value  of  the  power  sacrificed  by  loss  of 
head  against  the  expense  of  the  dispositions  necessary  for  pre- 
serving the  head,  viz.,  increased  cross-section  and  smoother 
perimeter.  In  a  canal  carrying  1 800  cubic  feet  per  second,  a 
loss  of  i  foot  head  would  involve  a  loss  of  1 50  horse-power, 
having  a  value  which  would  justify  considerable  expense  in 
avoiding  loss  of  head. 

When,  as  is  almost  universally  the  case,  the  water-power 
is  used  in  connection  with  steam,  and  the  demand  for  power 
largely  exceeds  the  low-water  flow  of  the  stream,  the  canal  is 
required  to  carry  a  varying  quantity  of  water.  In  the  season 


THE    VELOCITY  IN  CANALS.  351 

of  low  water  the  velocity  is  moderate  and  the  loss  of  head  is 
slight.  When  water  is  abundant  and  running  to  waste,  it 
carries  the  largest  possible  quantity  of  power  without  regard  to 
loss  of  head.  It  would  be  easy  to  construct  two  canals  of 
•equal  cross-section,  one  of  which  would,  with  equal  loss  of 
head,  deliver  twice  as  much  water  as  the  other.  It  would 
thus  appear  that  loss  of  head  is  of  primary  importance  in  the 
design  of  water-power  canals. 

In  considering  the  subject  of  Flowage,  page  8,  we  have 
used  the  rougher  and  more  approximate  method  of  computation 
by  the  formula 

v  —  c'irs, (56) 

in  which  v  =  the  velocity  in  feet  per  second,  .y  the  slope  of 
the  water-surface  in  feet  per  foot,  r  the  quotient  of  the  cross- 
section  divided  by  the  wetted  perimeter,  and  c  a  coefficient 
which  is  varied  according  to  judgment  to  suit  varying  condi- 
tions. In  computation  of  loss  of  head  in  canals  we  will  use 
Kutter's  formula,  which  is  thought  to  be  more  exact.  It  is  of 
the  same  form  as  (56),  but  c  is  a  variable  and  may  be  computed 
by  the  relation 

1.811        .00281 
41.66  +  -    -H 


--  ,    .00281  x»'   '      '      ' 

i  +  (41. 66  +  -^-)^ 

where  nis  a  numerical  quantity  depending  on  the  nature  of  the 
surface  in  contact  with  the  water.  It  is  called  the  coefficient 
of  roughness. 

For  straight  and  regular  channels  lined  with  planed 
boards  carefully  laid,  or  plastered  with  neat  cement, 
-  we  may  put  n  — OI° 

For  similar  channels  lined  with  unplaned  boards  or 
plastered  with  mortar,  or  for  the  best  and  cleanest 
brickwork , °12 


352  CANALS. 

Lining  the  boards  with  canvas  raises  the  value  of  n  to.  .  .015 
Channels  paved  and  walled,  best  work  .................  017 

"  "        "          "         roughest  work  .............  024 

Small  rivers  and  canals  with  fairly  regular  channels  in 

earth  ........................................  024 

Channels  in  earth  with  masonry  side  walls,  in  best  condi- 

tion ..................  .  ......................  020 

"          "     "       "          "  "        "      in  worst  con- 

dition ........................................  050 

Irregular  channels  in  earth  in  best  and  straightest  condi- 

tion ..................  .  ......................  025 

Do.  in  worst  condition,  obstructed  by  detritus  and  vege- 

tation ........................................  050 

In  exceptional  cases  n  rises  even  higher  than  the  latter 
figure. 

Channels  in  earth,  however  regular  they  may  be  on  com- 
pletion, will  fall  into  an  irregular  condition  in  the  course  of  a 
few  years,  with  a  corresponding  increase  in  the  value  of  n.  It 
is  the  latter  condition  that  must  be  assumed  in  computing  the 
flow. 

In  applications  (57)  takes  the  form 


(58) 


Irom  which  v  is  found  when  the  other  elements  are  known. 

v 
When    i>   is   known   c  is  readily  found,    being  —  —  -=.     Two 

Vrs 

other  cases  may  occur,  viz.  :  (i)  to  find  n  when  r,  s,  and  v  are 
known  ;  (2)  to  find  s  when  r,  n,  and  v  are  known.  We  will 
take  numerical  values  for  the  known  quantities,  which  makes 
the  equation  less  cumbrous,  while  the  principle  is  no  less 
obvious. 


THE    VELOCITY  IN  CANALS.  353 

Suppose  a  canal  in  which  r  =  12,  s  =  i  foot  per  mile  = 
*sfW»  v  =  3-29  feet  per  second,  what  would  be  the  value  of  »? 
Eq.  (58)  becomes 

56  50  +  T'811  6  1.811 

3'29  =     i+i6.3L    \/7^7'   or  69-Oi2  = 


56. 50«  4-  1.811 
or  69.012  =  i 


whence  69.012  x  i6.3i«*  -J-  12.512^  =  1.811, 

or  nz  -f-  -Oi  1 1  \6n  =.  .0016089, 

whence  by  the  ordinary  rule  for  quadratic  equations 


n  =  —  .005558  +  V. 0016089  -f-  (-OOSS6)2  =  -035. 

Again,  suppose  n  =  .035,  r  =  12,  v  =  3.29,  to  find  the 
value  of  s.  Inserting  these  values  in  (58),  it  becomes 

.0097341 
323,55**+- 

3.29=-  _£-_ 

,  .000028391 
1.42092  H — 

whence  we  obtain 

323- 55-r3  -  4-6748^  +  .0097341.?*  =  .00009341. 

This  is  a  cubic  equation  from  which  the  value  of  s  may  be 
obtained  by  the  rules  given  in  the  books  of  algebra. 

The  engineer  who  deals  with  these  problems  has  usually 
forgotten  most  of  his  algebra,  in  which  case  he  will  find  it  most 
convenient  to  obtain  the  value  of  s  by  a  process  of  trial  and 
error,  i.e.,  he  assumes  a  value  for  s  and  computes  the  several 
terms.  If  the  first  side  of  the  equation  exceeds  the  second, 


354  CANALS. 

the  assumed  value  of  s  is  too  great,  and  vice  versa.  He  amends 
his  supposition  and  tries  again  till  he  makes  both  sides  of  the 
equation  equal.  This  is  a  laborious  process,  but  is  usually  the 
one  to  be  adopted. 

Ganguillet  and  Kutter,*  in  the  work  referred  to,  give  a 
diagram  from  which  either  of  the  quantities  r,  s,  c,  or  n  can  be 
obtained  when  the  others  are  known.  Where  many  computa- 
tions of  this  kind  are  required  it  might  be  advisable  to  construct 
such  a  diagram.  It  is  seldom  necessary  to  obtain  r  from  the 
formula,  but  it  is  obvious  that  it  can  be  obtained  by  a  quadratic 
equation. 

Slope  of  Bottom. — The  bottom  of  a  canal  usually  receives 
a  slope  based  upon  some  assumed  delivery  of  water.  The 
slope  s,  determined  from  formula  (58),  is  assumed  to  apply  to 
both  the  surface  and  the  bottom.  If  the  slope  of  the  surface 
differs  materially  from  that  of  the  bottom,  the  velocity  and  the 
value  of  r  change  from  point  to  point.  In  fact  the  slope  of  the 
surface  never  is  precisely  the  same  as  that  of  the  bottom,  though 
usually  so  near  that  the  formula  applies  without  material  error. 
Problems  often  occur  in  which  serious  error  would  result  from 
assuming  the  depth  and  velocity  in  a  canal  to  be  uniform,  and 
it  is  necessary  to  take  account  of  the  variation  in  depth  conse- 
quent on  the  loss  of  head.  In  this  case  the  canal  must  be 
divided  into  a  number  of  parts  and  the  computation  applied 
separately  to  each  part.  After  computing  the  slope  and  loss 
of  head  in  the  first  part,  we  find  a  revised  cross-section,  a 
revised  velocity,  and  a  revised  value  of  r  applicable  to  the 
second  part,  and  so  on. 

Comparison  of  Smooth  and  Rough  Canals.  —Consider  two 
canals  of  the  same  cross-section,  the  same  mean  radius  r  = 
12.25,  tne  same  slope  s  =  .000256,  being  about  16  inches  in  a 
mile.  We  have  \^r  ^  3.5,  Vs  =  .016,  Vrs  =.  .056.  Sup- 
pose the  bed  and  banks  of  the  first  to  be  in  such  a  condition 


*  A   General    Formula   for   the   Flow  of  Water,   etc.     New  York,  John 
Wiley  &  Sons,  1889. 


COMPARISON  OF  SMOOTH  AND    ROUQH   CANALS.     355 

of  roughness  that  ^  =  .031,  which  would  be  no  uncommon 
case.  Suppose  the  second  to  be  straightened,  trimmed,  and 
lined  with  plank  so  that  n  =  .012.  Then  in  the  first  case 

41.66+58.42+10.98      ,—  - 

f;=-  -~-    1/12.25      X     .000256 

I     +    (41.66    +10.98)^- 

III.O6 

x  -°56  =  4-24- 

In  the  second  case 

41.66  +  150.92+10.98          ,• 


(41.  66+ 


.000256 


.  056  =  9.66. 


That  is,  according  to  admitted  principles,  the  second  canal 
would  carry,  with  the  same  loss  of  head,  more  than  twice  as 
much  water  as  the  first.  Such  a  velocity,  however,  could  only 
be  maintained  while  the  canal-surfaces  remained  perfectly  clean. 
It  would  diminish  as  the  latter  became  fouled  by  deposits. 
Moreover,  in  comparing  the  two  canals,  we  must  consider  not 
only  the  loss  of  head  incident  to  the  flow  of  the  water,  but  that 
necessary  to  impart  the  velocity.  This  would  be  for  the  first 
canal 


and  for  the  second 


so  that  the  first  canal  would  deliver  the  water  1.17  feet  higher 
than  the  second  and  would  have  that  much  advantage  in  point 
of  head. 


3$6  CANALS. 

To  compare  the  two  canals  on  the  supposition  that  the  total 
loss  of  head  is  the  same  in  each,  let  us  suppose  each  to  be  a 
mile  in  length.  Then  the  total  loss  of  head  in  the  first  case  is 
.000256  X  5280  +  0.28  =  1.63  feet.  By  eq.  (56)  we  have 

for   the    second    canal  c  =  — -=  =  ?! =172.5.     c  may  be 

Vrs       .056 

regarded   as   constant   for  any  slight  variation   in   depth  and 
velocity.      The  head  expended  in  imparting  the  velocity  v  is 

— ,  and  the  descent  in  the  canal  may  be  represented  by  5280^ 

=  ^280-:-,  so  that  we  have  the  total  loss  of  head 
0        * 


whence  v  =  \/ =  7.36. 

V  0.0301 

In  other  words,  the  second  canal  could  carry  74  per  cent 
more  water  than  the  first  with  the  same  total  loss  of  head. 

Effect  of  an  Ice-sheet. — The  capacity  of  a  canal  to  carry 
water  is  seriously  impaired  by  the  formation  of  a  sheet  of  ice, 
which  not  only  diminishes  the  cross-section,  but  increases  the 
wetted  perimeter.  There  is  a  lack  of  experimental  data  on 
this  subject,  and  it  is  not  known  what  value  of  n  applies  to  the 
ice-surface.  The  under  surface  of  the  ice  is  usually  corrugated 
and  irregular.  It  is  not  so  smooth  as  a  surface  of  planking, 
though  perhaps  smoother  than  a  wall  of  rubble  masonry.  In 
the  absence  of  exact  knowledge  we  will  use  the  value  of 
n  =  .024.  Assume  the  same  value  to  apply  to  the  rest  of  the 
perimeter.  Consider  a  channel  80  feet  wide  on  bottom,  12 
feet  deep,  side  slopes  2  to  I,  making  surface-width  128  feet; 
slope  i  foot  per  mile.-  Find  how  much  the  flow  would  be 
diminished  by  a  sheet  of  ice  floating  20  inches  deep. 


EFFECT  OF  AN  ICE-SHEET.  357 

In  the  open  channel  we  have 

Cross-section  =  (80  -j-  2  X  12)  X  12  =  1248. 
Perimeter  =  80  +  2  x  12  V~$  =  133.66. 
Radius  =r 


v=   41-66  +  75.46+  14., 


^9-34 
131.96 


1-4437 
Quantity  of  water  =  1248  X  3.84  =  4792  cubic  feet  per  sec. ' 

Head  required  to  impart  a  velocity  of  3.84  feet  per 

second 0.23  feet 

Loss  of  head  in  canal I  " 

Total  loss  of  head  in  canal  free  of  ice 1.23      " 

We  have  also 

3-84 


^5280 

In  the  case  of  the  canal  covered  with  an  ice-sheet  floating 
20  inches  deep,  we  have  the  cross-section 

=  (80  +  10.33  X  2)10.33  =  1039.8  square  feet, 
and  the  wetted  perimeter 

=  2  X  80  +  4  X  10.33  +  2  X  10.33  4/5"  =247. 5 1  feet 
Whence    we    have    for    the    mean     radius    r  —  4.20.       If  v 
represent  the  velocity  in    the    canal,    we    have  —  =  loss    of 


=  2.71,     Q  =  2.71  X  1039.8  =  2827.3. 


358  CANALS. 

V* 

head   at  entrance,   also  s  =  -y- ,  and  the  descent  in  the  canal 

z/2 
=  -y-  X  5280.      These  two  losses  must  be  equal  to  the  loss  in 

the  open  channel,  whence 


and 


That  is  to  say,  the  canal  frozen  over  to  the  depth  assumed 
would  carry  only  59  per  cent  as  much  water  as  the  open  canal 
with  the  same  loss  of  head.  Practically,  the  users  of  water, 
under  such  conditions,  would  not  confine  themselves  to  any 
prescribed  loss  of  head,  but  would  draw  as  much  water  as  they 
required,  or  as  much  as  they  could,  without  regard  to  loss  of 
head  and  consequent  diminution  of  their  fall.  But  the  utmost 
that  can  be  drawn  is  not  over  59  per  cent  of  what  could  be 
drawn  in  open  channel  with  equal  loss  of  head.  Where  there 
are  several  users  on  the  same  canal  it  often  happens  under 
these  conditions  that  the  water  at  some  hours  of  the  day  is 
entirely  drawn  out  of  the  canal  at  the  lower  end.  In  this  case 
a  singular  and  embarrassing  phenomenon  sometimes  occurs. 
The  ice-sheet  becomes  anchored  by  freezing  solidly  to  the 
bottom,  and  so  remains  when  the  water  comes  to  a  level  after 
the  stopping  of  the  mills  at  night.  During  the  night  a  fresh 
coating  of  ice  forms  and  is  in  its  turn  lowered  and  frozen  to  the 
anchored  sheet.  This  goes  on  till,  in  protracted  cold  weather, 
a  part  of  the  canal  is  packed  solidly  with  ice  from  top  to 
bottom. 

Lining  or  Sheathing  Canals. — In  the  above  comparison  of 
velocity  in  a  smooth  and  rough  canal,  page  354,  suppose  the 
cross-section  of  the  canal  to  be  1500  square  feet,  other  dimen- 
sions conformable  to  the  above  supposition.  Suppose  the  canal 


LINING    OR   SHEATHING    CANALS.  359 

to  supply  wheels  on  a  clear  head  of  30  feet.  We  have  found 
the  velocity  in  the  unlined  canal  4.24  feet  per  second,  corre- 
sponding to  a  flow  of  6360  cubic  feet  per  second,  and  in  the 
lined  canal  a  velocity  of  7.36,  corresponding  to  a  flow  of 
1 1  040.  Though,  for  reasons  stated,  we  could  hardly  hope  to 
reduce  n  to  .012,  there  is  little  doubt  that  by  reasonable 
expense  in  cleaning  the  canal  it  could  be  maintained  practically 
at  .01  5,  corresponding  to  a  velocity  of  6.64  and  a  flow  of  9960 
cubic  feet  per  second.  Here  is  a  gain,  due  to  the  improvement, 
of  3600  cubic  feet  per  second  in  the  delivery  of  the  canal.  In 
the  case  of  an  industry  which  has  attained  dimensions  far  in 
excess  of  the  low-water  flow  of  the  stream,  and  where  all  the 
users  are  provided  with  steam-engines,  this  additional  flow  of 
water,  though  it  may  not  be  obtainable  more  than  six  or  even 
four  months  in  the  year,  has  a  value  as  suspending,  for  the 
time  being,  the  consumption  of  coal  and  some  other  expenses 
of  steam.  Manufacturers  in  New  England  readily,  pay  three 
and  four  dollars  per  diem  per  mill-power  for  water  furnished  in 
this  manner.  As  the  above-mentioned  increase  of  3600  cubic 
feet  per  second  would  amount,  on  a  fall  of  30  feet,  to  some  144 
mill-powers,  it  is  readily  apparent  that,  under  suitable  condi- 
tions, a  very  large  outlay  would  be  justifiable  in  improving  the 
carrying  capacity  of  the  canal.  Improvements  of  this  character 
are  beginning  to  attract  the  attention  of  manufacturers.  As 
this  kind  of  work  has  not  been  practised  long  enough  to  estab- 
lish any  recognized  method  of  conducting  it,  the  writer  deems 
it  important  to  point  out  the  several  methods  that  may  be 
followed. 

i.   For  Cement  Work. — The  bed  and  slopes  of  the  canal 
being  finished  to  the  desired  grade,  the  slopes  not  steeper  than 

2  to    i,  the  whole  is   covered  with  a  layer  of  broken  stone 

3  inches  deep  on  the  slopes,  4  inches  on  the  bed.     This  is 
lightly  rolled  or  rammed  to  settle  it  into  the  earth  and  bring  it 
to  a  smooth  surface.     Cover  this  surface  with  a  layer  of  mortar 
not  so  stiff  as  would  be  used  for  masonry,  work  it  well  into  the 
•crevices  of  the  stone,  and  bring  it  to  a  smooth  surface.      Near 


CAXALS. 


the  water-surface,  within  the  range  of  ice  action,  the  protection 
must  be  heavier,  consisting  of  good  concrete  as  much  as  9  inches 
deep.  The  bottom  must  be  strong  enough  to  stand  the  occa- 
sional passage  of  carts  used  for  removing  deposits.  Near  the 
foot  of  the  slopes  numerous  weep-holes  must  be  left  to  prevent 
any  upward  pressure  when  the  canal  is  being  emptied. 

Where  the  canal  has  side  walls,  a  great  improvement  can 
be  made  by  simply  pointing  the  joints  of  the  masonry  with 
mortar ;  but  the  cost  of  a  facing  of  hard  brick  is  not  out  of  pro- 
portion to  the  benefit  to  be  expected.  This  may  be  one-half 
brick  thick,  backed  with  sufficient  mortar,  which  gets  a  good 
hold  by  being  worked  into  the  crevices  of  the  wall.  The 
rougher  the  wall,  provided  it  is  stable,  the  better  it  lends  itself 
to  this  method.  The  utmost  care  is  necessary  to  clean  the 
surfaces  of  the  stonework.  Openings  for  the  relief  of  pressure, 
near  the  foot  of  the  wall,  should  not  be  forgotten.  This  method 
could  only  be  adopted  in  the  southern  part  of  the  country, 
where  the  action  of  frost  is  not  severe. 

2.  For  Timber  Work. — The  plank  or  board  lining  must, 
of  course,  rest  on  sills  or  sleepers  imbedded  in  the  ground. 


FIG.  178. 

The  difficulty  is  to  prevent  the  work  from  rising  or  coming  into 
disarrangement  from  its  buoyancy.  Figs.  177  and  178  represent 
a  mode  of  confining  the  sills  which,  though  somewhat  expen- 
sive in  material,  is  expeditious  in  performance;  a  point  of  no 
small  importance  in  work  of  this  kind,  which  has  to  be  done 


LINING    OR   SHEATHING    CANALS.  561 

during  nights  and  holidays.  The  earthwork  being  finished,  the 
timbers  are  imbedded  in  trenches  cut  therein,  and  are  confined 
by  long  iron  rods  I  inch  diameter,  driven  through  holes  bored 
in  the  timbers.  The  length  of  these  rods  will  depend  on  the 
nature  of  the  material.  If  they  are  so  long  that  the  operation 
of  driving  will  form  a  sufficient  head  on  them,  they  will  have 
abundant  holding-power,  which  increases  with  time.  The  rods 
being  driven  and  the  earth  packed  around  the  sleepers  and 
brought  truly  up  to  their  surfaces,  the  planking  is  applied. 
This  may  be  2  inches  thick  at  the  bottom,  which  has  occa- 
sionally to  sustain  wheeled  vehicles,  and  i  or  I  \  inches  on  the 
slopes.  When  the  rod  is  put  in  position  for  driving,  its  head 
is  far  out  of  reach.  Fig.  179  shows  a  tool  for  starting  it  down- 


FIG.  179. 

ward.  To  a  piece  of  i|-inch  round  steel  18  inches  long  is 
welded  a  2-foot  length  of  pipe,  forming  a  cap,  which  is  slipped 
on  the  head  of  the  rod  before  it  is  erected.  The  rod  drives 
easily  for  the  first  3  or  4  feet,  and  the  cap  is  lifted  and  dropped 
by  any  convenient  tool,  as  a  shovel.  When  the  pipe  comes 
within  reach  of  the  hand  it  is  worked  more  expeditiously  till 
the  head  of  the  rod  comes  in  range  of  the  workman's  hammer. 
There  is  no  doubt  that  in  alluvial  ground  or  ground  favor- 
able to  driving,  wooden  stakes  can  be  driven  deep  enough  to 
hold  the  sleepers  with  safety.  This  can  readily  be  determined 
by  experiment,  i.e.,  by  driving  stakes  and  observing  the  force 
required  to  draw  them.  The  buoyancy  of  such  a  lining  would 
in  no  case  exceed  10  pounds  per  square  foot,  which  for  sleepers 
3  feet  apart  and  stakes  5  feet  is  about  150  pounds  pull  on  each 
stake.  This  diminishes  rapidly  as  the  timber  becomes  water- 
soaked.  In  this  method  it  is  better  to  use  3 -inch  by  8 -inch 
joists  for  the  sleepers.  These  are  laid  flatwise  and  bored  with 
3 -inch  holes  for  the  stakes,  which  are  formed  with  heads  that 
do  not  go  through  the  holes. 


362 


CANALS. 


Figs.  1 80  and  181  represent  another  method  of  lining- 
which  may,  under  some  conditions,  be  used  with  advantage, 
especially  when  the  ground  is  not  adapted  to  driving,  as,  for 
instance,  where  the  bed-rock  is  not  far  enough  below  bottom. 
The  surface  of  the  canal,  bed,  and  slopes,  being  finished  to 
subgrade,  is  covered  with  boards  or  planks  running  lengthwise 
of  the  canal.  These  are  not  necessarily  of  uniform  length, 
.width,  or  thickness.  Provided  they  are  sound,. they  may  be 


FIG.  i8c. 


FIG.   iSr. 

refuse  lumber,  culls,  slabs,  lumber  taken  from  coffer-dams  or 
old  buildings.  On  this  covering  are  laid  the  sleepers,  consist- 
ing of  2  X  9  or  3  X  9  plank  set  edgewise  and  confined  by  toe- 
nailing,  i.e.,  by  nails  driven  obliquely  through  the  lower 
corners  into  the  covering.  These  nails,  crossing  each  other, 
have  a  sufficient  holding  power.  The  spaces  or  pockets 
between  the  sleepers  are  then  filled  with  gravel  or  whatever 
material  occurs  in  the  canal,  which  material  is  placed  in  posi- 
tion, tamped,  and  levelled  even  with  the  tops  of  the  sleepers. 
Then  the  lining-plank  are  applied.  In  applying  this  method 


LINING    OR   SHEATHING   CANALS.  363 

to  an  existing  canal,  the  material  excavated  in  front  of  the 
work  is  brought  back  and  dumped  into  the  pockets.  Holes 
must  be  bored  through  the  lining  near  the  foot  of  the  slopes  for 
relief  of  pressure.  In  applying  a  timber  lining  to  a  canal  with 
side  walls,  the  bottom  is  treated  by  either  of  the  methods 
pointed  out,  and  light  timbers  are  bolted  to  the  side  walls  to 
receive  the  planking. 


CHAPTER    XVII. 
DEVELOPMENT   OF   NATURAL  WATER-POWERS. 

Two  general  methods  of  applying  water-power  are  now  in 
use.  The  first,  which  is  the  method  adopted  in  all  the  old 
manufacturing  centres,  consists  in  conducting  the  water  by 
means  of  canals  to  the  several  establishments  requiring  power. 
In  the  second,  the  whole  operation  of  converting  the  water  into 
mechanical  power  and  the  latter  into  a  form  suitable  for  trans- 
mission is  performed  in  a  single  establishment  called  a  power- 
house, whence  it  is  transmitted  to  the  several  users.  The  first 
requires  the  mills  to  be  located  in  situations  accessible  to  the 
,  water,  and  often  calls  for  greater  expense  in  their  construction 
than  would  otherwise  be  necessary.  The  second  carries  the 
power  to  the  machines,  which  are  located  according  to  con- 
venience and,  thereby  adapting  itself  to  the  multifarious  require- 
ments of  industry,  it  has  found  application  in  many  if  not  most 
of  the  recent  installations.  Shafting,  wire  rope,  air,  and  water 
under  pressure  have  found  wide  application  for  conveying 
power  from  water-wheels  to  the  machines,  but  since  the  great 
development  of  electricity  dating  from  about  1880,  this  agent 
has  taken  the  leading  place  as  a  means  of  transmitting  power. 
Fig.  182  represents  a  common  arrangement  for  a  single 
mill  on  a  small  stream.  The  dam  forms  the  foundation  for  the 
upper  end  of  the  mill,  and  the  mill  forms  one  abutment  of  the 
wasteway,  the  opposite  abutment  being  connected  by  an  em- 
bankment with  the  high  ground.  At  the  upper  end  of  the  mill 
is  a  wooden  platform  raised  above  the  level  of  high  water. 
Here  are  located  the  gates  for  admitting  water  to  the  wheels. 

364 


APPLYING    WATER-POWER. 


This  arrangement  assumes  that  all  the  fall  in  the  vicinity  is 
utilized  by  the  dam.  In  other  words,  that  there  is  quiet  water 
for  some  distance  below  the  dam. 


Mill     Pond 


FIG.  182. 

Fig.  183  indicates  the  arrangement  suited  to  the  case  of 
rapids  below  the  dam,  which  it  is  desirable  to  include  in  the 
fall  acting  on  the  wheels,  or  the  case  of  a  number  of  mills 
occupying  too  much  ground  to  admit  of  drawing  directly  from 
the  pond.  A  canal  leads  from  the  mill-pond  to  a  point  below 
the  rapids,  or  to  ground  favorable  to  the  location  of  mills. 
Sometimes,  instead  of  extending  the  canal,  the  river-bed  can 
be  deepened,  or  a  separate  tail-race  constructed  leading  down- 
stream far  enough  to  comprehend  the  entire  fall.  It  is  desir- 
able in  that  case  to  exclude  the  flood-waters  from  the  tail-race, 
otherwise  it  is  filled  and  rendered  inoperative  in  time  of  high 
water.  A  canal  such  as  is  here  contemplated  generally  has 


366      DEVELOPMENT  OF  NATURAL    WATER-POWERS. 

a  waste  way  at  the  lower  end.  This  is  necessary  when  the 
canal  has  considerable  length  and  supplies  a  number  of  mills, 
in  order  to  prevent  a  dangerous  surge  of  the  water  when  the 
mills  stop,  as  they  often  do,  at  the  stroke  of  a  bell.  The  water 
in  the  canal  continues  to  move  after  the  gates  are  closed,  and 
unless  a  vent  is  provided  the  momentum  of  the  water  causes  it 
to  overflow  the  banks.  In  northern  latitudes  a  wasteway  is 


FIG.   183. 

necessary  to  sluice  off  the  ice  and  prevent  its  accumulation  in 
the  canal. 

Fig.  1830  represents  the  arrangement  of,  and  mode  of 
applying  the  water  to,  a  modern  cotton-mill.  A  is  a  long, 
low  building  parallel  to  the  canal  and  near  it,  containing  the 
repair-shop,  storerooms,  offices,  baling-  and  packing-rooms; 
B,  cotton  storehouse;  C,  one  of  the  main  mills,  generally  five 
or  six  stories  high.  The  small  circles  represent  the  wheel- 
pits.  The  water  leaves  the  canal  at  D,  and,  after  passing 
through  a  covered  chamber  called  the  "feeder-head,"  is 
admitted  to  the  penstocks  through  gates  E  E.  After  passing 
the  wheels,  the  water  is  discharged  through  arched  culverts 
into  the  open  race  G.  A  projection  on  the  front  face  of  the 
mill  contains  the  entrance  and  stairways.  A  projection  on  the 


APPLYING    WATER-POWER. 


367 


rear  contains  the  sinks  and  lavatories.  When  health  laws  do 
not  intervene  these  discharge  directly  into  the  culverts.  H  is 
the  engine-house,  K  the  boiler-house,  L  the  chimney.  The 
wheels  and  engine  give  motion  to  a  main  shaft,  running  along 
the  basement.  Each  of  these  motors  can  be  thrown  in  or  out 
of  connection  at  will.  The  projection  F  is  the  belt-house,  con- 
taining the  belts  which  transmit  motion  from  the  main  line  of 
shafting  to  the  several  lines  in  the  rooms  above.  In  times  of 
abundant  water  the  engine  does  not  run.  It  is  coupled  on 


C 

E 

"S-  

n 

[L~_~L1 

:  : 
o 

E 

:  I 

1 


FIG.  1830. 


when  the  flow  of  the  stream  falls  short  of  the  demand,  and 
furnishes  a  larger  and  larger  supply  of  power  as  the  flow  of  the 
stream  diminishes  until,  in  the  lowest  stage,  the  mills  often  run 
almost  wholly  by  steam.  The  water  from  the  canal  enters  the 
feeder-head  through  a  line  of  rack,  and  at  D  is  a  platform  on 
which  workmen  can  stand  to  rake  out  the  trash  which  accumu- 
lates in  the  racks. 

Fig.  184  shows  a  case  in  which  the  fall  in  a  wide  stretch 
of  river  can  be  utilized  by  a  short  canal.  Such  a  situation 
occurs  on  the  Cedar  River,  at  Waterloo,  Iowa,  and  works  for 
development  of  power  were  undertaken  there  in  1883.  The 


368      DEVELOPMENT   OF  NATURAL    WATER-POWERS. 

writer  was  consulted  as  to  the  general  arrangement  and  scheme 
of  these  works.  The  promoters  of  the  enterprise  had  built  a 
dam  as  indicated,  raising  a  head  of  about  6  feet,  and  had  con- 
structed head-gates  at  the  entrance.  They  had  excavated  the 
canal,  which  was  about  2  miles  long,  to  a  depth  sufficient  to 
allow  the  water,  as  raised  by  the  dam,  to  flow  through.  There 
was  a  fall  of  about  2  feet  3  inches  in  the  long  bend  of  the  river. 
They  conceived  the  idea  of  excavating  the  canal  by  the  scour- 
ing power  of  the  water,  the  formation  being  of  a  character 
favorable  to  this  action.  Their  intention  was  to  use  the  canal 


FIG.  184. 

as  a  tail-race,  placing  the  mills  at  the  upper  end.  Their  atten- 
tion was  strongly  called  to  the  greater  probability  of  success  if 
they  placed  the  mills  at  the  lower  instead  of  the  upper  end  of 
the  canal,  making  the  canal  serve  as  a  head-race  instead  of  a 
tail-race,  as,  in  the  former  case,  it  would  not  need  to  go  so  deep 
by  something  over  8  feet  as  in  the  latter.  The  desire  to  place 
the  mills  near  the  existing  centre  of  population  prevailed  over 


LOWELL,    MASS. 


369 


the  engineering  considerations.  They  were  unable  to  excavate 
the  race  to  the  required  depth  by  the  proposed  method,  and 
the  insufficiency  of  the  tail-race  has  made  the  water-power  of 
little  value. 

Fig.  185  indicates  the  general  arrangement  of  canals  at 
Lowell,*  Mass.     The  extreme  fall  here  is  now  near  40  feet, 


FIG.  185. 

having  been  recently  increased  several  feet  by  deepening  the 
Merrimack  River  below  the  mouth  of  the  Concord.  The  dam 
crosses  the  river  in  a  zigzag  line  at  e  at  the  head  of  a  series  of 
rapids  which  extend  down  to  the  bend  in  the  river.  I  I  I  is  the 
old  Pawtucket  canal,  built  originally  for  purposes  of  navigation. 

*  Tenth  Census  Report  U.  S.,  vol.  xvi.     Water-power  of  Eastern  New 
England,  p.  31.  • 


3/0      DEVELOPMENT  OF  XATURAL    WATER-POWERS, 

It  has  a  gate-house  near  its  head  containing  five  9-foot  gates, 
which  are  controlled  by  hydraulic  pressure,  each  gate  being 
attached  directly  to  the  piston  of  a  hydraulic  cylinder,  which 
is  supplied  by  pipes  from  the  company's  fire-reservoir.  5  5  is 
the  northern  canal,  of  more  recent  construction.  It  is  of  rect- 
angular section,  100  feet  \vide  and  i  5  to  20  feet  in  depth,  and 
is  controlled  by  head-gates  at  the  dam,  the  gate-house  forming 
a  part  of  the  dam.  There  are  ten  gates,  each  8  feet  wide  and 
capable  of  a  lift  of  1 5  feet.  These  gates  are  raised  and  lowered 
by  long  screws  passing  through  nuts,  which  are  turned  by 
means  of  a  system  of  shafting,  belts,  and  pulleys  driven  by  a 
small  turbine.  5  6  is  the  western  canal,  which  is  in  communi- 
cation with  the  northern  and  also  with  the  Pawtucket  canal. 
7  8  supplies  the  Lowell  Machine-shop  and  the  Lowell  Carpet- 
mills,  which  both  discharge  "into  2  2  with  a  fall  of  about  1 3  or 
14  feet,  also  the  Merrimack  Mills,  which  discharge  into  the  river 
with  the  total  head.  The  northern  canal  supplies  the  Tremont 
and  Suffolk  Mills,  which  discharge  into  6  6  with  a  fall  of  some 
1 3  feet.  6  6'  supplies  the  Lawrence  Mills,  which  discharge  into 
the  river  with  the  remaining  fall.  3  3  supplies  the  Appleton 
and  Hamilton  Mills  under  a  head  of  some  I  3  feet,  discharging 
into  2  2.  This  latter  canal  supplies  the  Booth  and  Massachu- 
setts Mills  and,  in  part,  the  Middlesex,  all  discharging  into  the 
Merrimack  or  Concord  rivers.  The  northern  and  western 
canals  are  connected  with  the  Merrimack  canal  by  an  under- 
ground feeder  on  the  line  9  9.  Water  falls  from  the  basin  3.1  7 
into  the  canal  2  2  over  a  wasteway  controlled  by  flashboards. 
Water  is  also  discharged  into  the  canal  6  6  over  a  wasteway 
at  T,  and  similar  wasteways  discharge  the  surplus  water  from 
each  of  the  lower-level  canals  into  the  river.  These  wasteways 
are  essential  in  order  to  maintain  the  required  level  in  the 
canals,  since  the  discharge  from  the  upper  mills  may  greatly 
exceed  or  fall  short  of  the  draft  of  the  mills  on  the  lower  level, 
and  means  must  be  provided  for  discharging  the  excess  and 
supplying  the  deficiency.  These  wasteways  are  under  the  con- 
stant care  of  attendants,  who  remove  and  replace  the  flashboards- 


HOLYOKE,    MASS.  371 

according  to  the  stage  of  water  in  the  canal.      The  Merrimack 
Mills  located  at  A  use  the  water  under  the  full  head. 

Fig.  1 86  shows  the  arrangement  of  canals  at  Holyoke, 
Mass.  The  total  fall  here,  from  the  pond  above  the  dam  to 
quiet  water  below,  is  near  60  feet.  The  working  fall  is  50  feet 
and  upward,  according  to  trie  stage  of  the  river.  The  fall  is 
divided  into  three  parts  by  the  canals  1,2,  3,  No.  I  being 
the  upper  level,  2  the  second,  3  the  third.  In  describing  these 
canals  we  cannot  do  better  than  use  the  language  of  Professor 
Swain  in  the  Tenth  Census  Report,  vol.  XVI :  "The  system  of 
•canals  at  Holyoke  comprises  three  levels  from  which  water  is 
drawn.  The  first  or  upper  level  strikes  off  across  the  bend 
which  the  river  forms,  and  runs  at  a  distance  of  from  2800 
to  3400  feet  from  the  latter ;  it  has  a  length  of  5700  feet  at 
present"  (1880,  since  extended  some  250  feet),  "and  de- 
creases in  width  from  150  feet  near  the  bulkhead  to,  say, 
105  feet  at  the  lower  end.  The  water-depth  is  about  20  feet 
near  the  bulkhead,  but  through  the  main  portion  of  the  canal 
is  uniformly  about  10  feet.  The  canal  is  walled  throughout 
its  length  to  a  height  generally  of  2  or  3  feet  above  the  water- 
surface,  and  is  the  only  one  of  the  three  canals  that  has  been 
completely  walled.  The  fall  from  this  level  to  the  second  is 
20  feet.  Near  the  upper  end  a  few  mills  discharge  from  it 
directly  into  the  river,  using  falls  of  32  to  40  feet.  The  second 
level  runs  parallel  to  the  first  and  400  feet  nearer  the  river, 
forming  a  straight  reach  of  6500  feet;  continuing  from  the 
upper  end  it  also  sweeps  around  through  a  further  distance 
of  2600  feet  at  present,  running  parallel  to  the  curving  course 
of  the  river  and  500  feet  distant  from  it.  Its  width  decreases 
from  I  50  feet  at  the  upper  end  to  90  feet  at  the  lower  end  of 
the  straight  reach,  and  in  the  curving  portion  lies  mainly 
between  140  and  150  feet.  The  water-depth  in  this  level  is 
•uniformly  about  8  feet.  The  supply  of  water  comes  from  the 
first  level,  partly  as  tail-water  from  the  mills  and  partly  from 
the  waste-weir  and  gates  between  the  two  levels.  The  fall  to 
the  third  level  is  n£  or  12  feet,  and  from  the  second  level  to 


372  DEVELOPMENT  OF  NATURAL    WATER-POWERS. 


HO L  YOKE,   MASS,  373 

the  river  from  25  to  28  feet.  The  third  level,  for  a  part  of  its 
course,  runs  parallel  to  the  river,  at  a  distance  from  it  of,  say, 
500  feet.  It  has  a  total  length  of  from  3500  to  4000  feet,  a 
width  of  about  100  feet,  and  a  water-depth  of  8  feet.  The  fall 
from  this  level  to  the  river  is  substantially  the  same  for  all  the 
mills  using  it,  but,  according  to  the  stage  of  the  river,  ranges 
from  15  to  27  feet.  In  addition  to  the  wasteway,  already 
described,  near  the  bulkhead,  having  a  length  of  about  2OO 
feet,  and  discharging  into  the  river,  there  is  another,  of  40  feet, 
over  which  water  descends  from  the  first  to  the  second  level. 
Closely  adjacent,  the  second  level  has  a  waste- weir  100  feet 
long,  toward  the  river,  which  the  overflowing  water  reaches 
through  four  arched  openings  underground.  At  the  lower  end 
of  the  second  level  there  is  another  weir,  80  feet  long,  over 
which  water  spills  to  the  third  level.  The  latter  has  a  similar 
weir,  i  50  feet  long,  connecting  with  the  river.  These  various 
weirs  do  not  rise  to  the  ordinary  level  of  the  water-surface,  but 
are  surmounted  by  temporary  flashboards,  varying  from  18 
inches  to  2  and  even  3  feet  in  height,  used  for  maintaining  the 
proper  level.  At  each  weir  there  are  also  waste-gates  at  or 
near  the  bottom,  which  may  be  used  in  connection  with  the 
flashboards  for  regulating  the  level  or  for  drawing  it  down 
altogether. 

' '  On  the  left  bank  of  the  river  is  a  short  canal,  4,  which 
supplies  three  mills  under  a  head  of  about  35  feet,  discharging 
directly  into  the  river.  This  is  controlled  by  a  small  gate- 
house. 6  is  the  gate-house  on  the  right  bank.  It  is  about  40 
feet  wide,  measured  with  the  current,  and  has  twelve  gate- 
openings,  each  8  feet  wide  by  15  feet  deep,  separated  by  piers 
about  19  inches  thick;  and  also  two  smaller  gate-openings, 
each  4^  feet  wide  by  io£  feet  deep.  This  is  surmounted  by  a 
brick  building  in  which  is  the  machinery  for  working  the  gates. 
The  power  is  furnished  by  a  turbine  at  one  end  of  the  building 
which  acts  directly  to  turn  a  long  horizontal  shaft  running 
lengthwise  of  the  building  above  the  gates.  Each  of  the  latter 
has  two  vertical  wooden  posts  (stems),  10  by  13  inches  in  size, 


374      DEVELOPMENT  OF  NATURAL    WATER-POWERS. 

fastened  to  it,  and  faced  on  one  side  with  iron  racks.  The 
long  shaft  operated  by  the  turbine,  in  turn,  by  connecting 
belts,  causes  a  series  of  cog-wheels  to  revolve,  the  last  of  these 
engaging  and  moving  the  racks  already  mentioned  and  with 
them  the  gates,  each  of  which  can  be  moved  independently  of 
every  other.  Commonly  the  water  stands  higher  outside  the 
gates  than  in  the  canal ;  at  such  times  they  are  not  raised  to 
the  full  height,  and  in  consequence  of  the  pressure  power  is 
required  to  close  them;  but  in  low  water  the  gates  are  raised 
entirely  above  the  surface,  and  their  weight  alone  is  sufficient 
to  close  them. 

"  Adjacent  to  the  bulkhead  and  forming  the  river-wall  of 
the  main  canal  is  a  wasteway  198^  feet  long;  it  is  constructed 
of  solid  masonry,  and  rises  to  within  20  or  24  inches  of  the  top 
of  the  gate-openings  in  the  bulkhead ;  for  the  remaining  height 
above  its  crest  the  water  in  the  canal  is  controlled  by  temporary 
flashboards.  Of  the  198!-  feet  of  length,  40  feet  rises  above 
the  surface  of  the  water  in  the  canal,  and  about  5  feet  above 
the  crest  of  the  waste-weir  proper.  This  portion  is  pierced  by 
four  waste-gates,  their  centres  about  20  feet  below  the  normal 
water-surface  in  vthe  canal ;  these  gate-openings  measure  5  feet 
in  width,  and  from  *5  feet  to  65  inches  in  depth." 

The  principal  industry  carried  on  at  Holyoke  is  paper- 
making,  in  which  the  heavier  machines  run  twenty-four  hours 
a  day. 

Fig.  187  shows  the  arrangement  of  canals  at  Lawrence, 
Mass. ,  where  the  plan  of  development  was  simpler  than  in  the 
cases  just  described.  The  total  fall  here  is  31  feet,  and  the 
practical  working-head  in  ordinary  stages  of  the  river  is  26  to 
30  feet,  subject  to  considerable  diminution  in  times  of  high 
water.  A  canal  on  each  side  of  the  river  starts  at  the  dam  and 
leads  down-stream.  That  on  the  north  side,  which  is  the  prin- 
cipal one,  is  5330  feet  long,  100  feet  wide  at  the  upper  end,  and 
60  at  the  lower  end,  with  the  cross-section  shown  in  Fig.  188. 
Its  depth  is  12  feet  in  the  middle,  4  feet  at  the  side  walls,  and 
the  bottom  is  graded  to  a  fall  of  I  foot  in  10000,  or  0.53  foot 


LAWRENCE,  MASS. 


375 


i — 

f 


DEVELOPMENT  OF  NATURAL    WATER-POWERS. 


DIVISION  OF  FALL.  377 

in  the  length  of  the  canal.  The  head-gates  are  twenty-four  in 
number,  arranged  in  six  sets  of  four  each,  or  closing  six  sluice- 
ways between  piers  12  feet  deep  and  9  feet  wide,  so  that  each 
gate  is  3  feet  high  and  7  feet  long.  They  are  operated  by 
hand.  This  improvement  was  made  subject  to  the  legal 
obligation  of  providing  for  the  passage  of  boats.  There  is  a 
lock  of  slight  lift  at  the  head  of  the  canal,  and  a  flight  of  three 
locks  descending  into  the  river  at  the  foot;  also  a  wasteway 
by  which  the  canal  may  be  emptied  into  the  Spicket  River, 
which  here  joins  the  Merrimack.  There  is  no  division  of  the 
fall ;  the  mills  are  placed  between  the  canal  and  river,  drawing 
from  the  former  and  discharging  into  the  latter.  At  a  distance 
of  about  80  feet  from  the  canal  a  line  of  sheet-piling  extends 
parallel  to  it  for  nearly  half  its  length  to  prevent  percolation, 
the  bank  being,  to  a  considerable  extent,  artificial. 

The  south  canal  was  built  in  1866,  and  carried  for  a  dis- 
tance of  2OOO  feet  with  a  rectangular  section  60  feet  wide  and 
10  feet  deep.  It  has  since  been  extended  750  feet.  The 
head-gates  are  sixteen  in  number,  in  four  sets,  and  are  operated 
by  hand.  It  is  intended  to  extend  this  canal  as  the  demand 
for  power  increases. 

The  plan  of  dividing  the  fall  into  two  or  three  parts  was 
adopted  at  Lowell  and  Holyoke  with  the  view  of  commanding 
as  large  an  area  of  ground  as  possible  for  the  placing  of  mills 
and  appurtenant  buildings.  It  is  a  "precedent  that  will  probably 
not  be  followed  in  any  future  plan  of  development.  The  supply 
from  one  level  cannot  adjust  itself  to  the  demand  of  the  next, 
and  much  water  is  necessarily  wasted  uselessly  from  one  to  the 
other.  Moreover,  the  tendency  of  modern  manufacturing  is 
constantly  toward  more  rapid  velocities,  which  makes  it  more 
profitable  to  use  a  high  head  than  two  or  three  low  heads, 
since  the  lower  the  head  the  more  expensive  and  cumbrous  is 
the  mechanism  required  to  bring  up  the  velocity  to  the  rate 
required  by  the  manufacture.  As  between  two  wheels  of  the 
same  diameter,  the  velocity  of  the  circumference  will  be  as  the 
square  root  of  the  head,  but  the  wheel  on  the  lesser  head,  in 


3/8      DE  VELOPMENT  OF  NA  TURAL    WA  TER-PO  WERS. 

order  to  draw  the  same  quantity  of  water,  must  have  a  larger 
diameter  than  the  other.  Therefore,  a  wheel  on  a  1 2-foot 
head  will  not  make  more  than  half  as  many  turns  per  minute 
as  a  wheel  drawing  the  same  quantity  of  water  on  a  24-foot 
head.  A  wheel  on  a  24-foot  head  gives  2.83  times  as  much 
power  as  the  same  wheel  on  a  1 2-foot  head,  and  it  would  prac- 
tically require  three  wheels  on  the  latter  head  to  give  the  same 
power  as  one  on  the  former.  Moreover,  on  every  application 
of  water  to  wheels  there  is  a  loss  in  penstock  and  race  usually 
estimated  at  about  i  foot.  A  head  of  60  feet  used  entire  is  an 
effective  head  of  59  feet,  but  if  divided  into  three  parts  it  is  an 
effective  head  of  only  57,  and  in  the  latter  case  we  require 
more  than  four  times  as  much  weight  of  wheel,  penstock,  case, 
shafting,  and  gearing  to  develop  a  given  amount  of  power  as 
in  the  former.  The  reason  above  given  for  dividing  the  head 
in  the  earlier  developments,  viz.,  as  a  means  of  distributing  the 
power  over  an  extended  factory  district,  has  lost  much  of  its 
force  by  recent  developments.  The  power  conveyed  by  a 
canal  100  feet  in  width  can  now  be  carried  by  a  3O-inch  pipe 
buried  in  the  ground,  or  by  a  copper  wire  occupying  no  appre- 
ciable space.  For  these  reasons  we  seldom  hear  in  water- 
power  projects  of  the  present  day  of  any  suggestion  for  divid- 
ing the  head. 

The  above  considerations  explain  why  very  low  falls  are 
hardly  considered  worthy  of  development  or  maintenance  at 
the  present  day.  The  numerous  abandoned  mill  privileges 
met  with  throughout  New  England  have  generally  very  low 
falls.  The  expense  of  installing  water-wheels  on  a  fall  of 
6  feet  is  actually  greater  for  the  same  quantity  of  water  than 
on  a  fall  of  24  feet,  while  the  power  is  less  than  one-fourth  as 
great.  Such  a  fall  can  often  be  incorporated  with  the  next  fall 
on  the  stream  above  by  removing  the  dam  and  deepening  the 
channel,  or  with  the  next  fall  below  by  raising  that  dam  and 
flowing  it  out.  This  is  usually  a  more  profitable  use  than  any 
separate  scheme  of  development. 


CHAPTER    XVIII. 
TRANSMISSION   OF   POWER. 

THE  points  at  which  water-power  can  be  most  economically 
developed  are  often  more  or  less  remote  from  those  at  which  it 
is  required.  In  the  plans  of  development  thus  far  described, 
the  mills  are  forced  into  locations  accessible  to  the  water 
flowing  by  gravity,  and  their  construction  is  thereby  often 
rendered  much  more  expensive  than  it  would  be  if  their  location 
could  be  chosen  upon  other  considerations.  Many  large 
water-powers  lie  undeveloped  within  a  few  miles  of  centres  of 
industry  and  population  having  unlimited  use  for  power.  The 
transmission  of  power,  therefore,  has  an  intimate  connection 
with  the  subject  of  water-power. 

Shafting  is  used  to  transmit  power  from  one  part  of  a  mill 
or  shop  to  another,  and  is  sometimes  employed  for  external 
transmission  to  distances  of  a  few  hundred  feet.  Beyond 
300  or  400  feet  it  becomes  too  expensive  as  compared  with 
wire  rope.  Shafting  consists  of  a  line  of  round  iron  or  steel 
bars  rigidly  fastened  together,  resting  in  bearings  which  permit 
it  to  rotate,  and  carrying  the  organs  for  delivery  of  power. 
Shafting  is  made  in  lengths  of  12  to  24  feet,  the  latter  being 
as  long  as  can  be  conveniently  handled  and  transported ;  but 
the  largest  mills  can  produce  lengths  up  to  40  feet  if  desired. 
It  is  now  almost  universally  made  of  steel,  by  rolling,  and 
hardened  on  the  exterior  by  compression.  It  is  usually  turned 
to  an  exact  cylindrical  surface  for  the  convenient  application 
of  its  attachments,  and  in  situations  exposed  to  view  is 
smoothed  by  polishing.  Coupling-plates,  gears,  and  pulleys 
are  fixed  by  keys,  which  are  short  prismatic  pieces  of  hardened 

379 


380  7'AAA'SMISSION   OF  POWER. 

steel  driven  into  grooves,  called  seats  or  splines,  cut  partly  m 
the  shaft  and  partly  in  the  attachment.  The  separate  pieces 
of  shafting  are  united  into  one  continuous  line  of  shafting  by 
couplings  of  various  forms,  a  standard  form  consisting  of  two 
circular  plates  keyed  to  the  ends  that  are  to  be  united  and 
fastened  to  each  other  by  bolts.  James  B.  Francis,  from  an 
experimental  inquiry  made  in  1867,  deduced  the  following  table 
(Table  6)  of  the  diameters  of  shafting. 

The  table  gives  the  power  which  can  be  safely  carried  by 
shafts  making  100  turns  per  minute.  The  power  which  can 
be  carried  by  the  same  shaft  at  any  other  velocity  may  be 
found  by  the  following  simple  rule : 

Multiply  tJie  power  given  in  tlie  table  by  tJie  number  of 
revolutions  of  the  shaft  per  minute,  and  divide  the  product  by 
100;  the  quotient  will  be  the  power  which  can  be  safely 
carried. 

The  table  for  steel  shafts  contemplates  the  best  quality  of 
steel.  Makers  of  the  present  day,  using  the  metal  that  passes 
in  the  trade  for  steel,  make  the  diameters  about  6  per  cent 
greater.  For  wrought  or  cast  iron  the  table  gives  ample 
dimensions.  In  shafting  which  both  transmits  power  and  dis- 
tributes it  along  the  line  the  losses  are  considerable.  In  many 
cotton-mills  not  more  than  75  per  cent  of  the  power  furnished 
by  the  motors  reaches  the  machines,  the  remainder  being 
absorbed  in,  resistance  of  shafting,  belts,  and  gearing.  In  a 
line  used  wholly  for  transmission  without  any  intermediate 
delivery  the  loss  should  not  exceed  3  per  cent  in  100  yards. 

In  modern  mills  and  factories  the  lines  of  shafting  are  sup- 
ported by  bearings,  usually  about  10  feet  apart.  In  a  line 
used  wholly  for  transmission,  the  intervals  may  be  "much 
greater.  Mr.  Francis  gives  the  following  as  the  greatest 
admissible  distance  between  the  bearings  of  a  continuous  shaft, 
which  carries  no  attachments  other  than  the  couplings.  The 
figures  relate  to  steel  shafting,  but  they  would  be  substantially 
the  same  for  wrought  iron.  The  two  end  intervals  should  be 
considerably  less  than  those  given. 


SHAFTING. 


381 


TABLE   6. 


. 

Horse-power  which  can  be  safely  car- 
ried by  shafts   for   prime  movers  and 
gears,  well  supported  by  bearings  and 
making  100  revolutions    per    minute, 

Horse-power  which  can  be  safely  trans- 
mitted by  shafts  making  100  revolu- 
tions per  minute,  in  which  the  trans- 
verse strain,  if  any,  need  not  be  con- 

Diameter 

if  of 

sidered,  if  of 

of  Shaft 

Wrought 
Iron. 

Steel. 

Cast  Iron. 

Wrought 
Iron. 

Steel. 

Cast  Iron. 

I.OO 

1.0 

1.6 

0.6 

2.O 

3-2 

1.2 

1.25 

2.0 

3-1 

1.2 

3-9 

6.2 

2-3 

1.50 

3-4 

5-4 

2.O 

6.7 

10.8 

4.1 

5-4 

8.6 

3-2 

10.7 

17.2 

6-4 

2.0O 

8.0 

12.8 

4.8 

16.0 

25.6 

9.6 

2.25 

11.4 

18.2 

6.8 

22.8 

36.4 

13-7 

2.50 

15.6 

25.0 

9-4 

31-2 

50.0 

18.7 

2-75 

21 

33-3 

12.5 

41.6 

66.6 

25.0 

3-oo 

27 

43 

16 

54 

86 

32 

3-25 

34 

55 

21 

69 

no 

41 

3-50 

43 

69 

26 

86 

137 

51 

3-75 

53 

84 

32 

105 

169 

63 

4.00 

64 

IO2 

38 

128 

205 

77 

4-25 

77 

123 

46 

154 

246 

92 

4-50 

I46 

55 

182 

292 

109 

4-75 

107 

171 

64 

214 

343 

129 

5-oo 

125 

2OO 

75 

250 

400 

150 

5-25 

232 

87 

289. 

463 

174 

5.50 

166 

266 

TOO 

333 

532 

200 

5-75 

190 

304 

114 

380 

608 

228 

6.00 

216 

346 

130 

432 

691 

259 

6.25 

244 

391 

I46 

488 

781 

293 

6.50 

275 

439 

165 

549 

879 

330 

6-75 

308 

492 

185 

615 

984 

369 

7.00 

343 

549 

206 

686 

1098 

412 

7-25 

38i 

610 

229 

762 

1219 

457 

7-50 

422 

675 

253 

844 

1350 

506 

7-75 

465 

745 

279 

931 

1490 

559 

8.00 

512 

819 

307 

1024 

1638 

614 

8.25 

898 

337 

1123 

1697 

674 

8.50 

614 

983 

368 

1228 

1965 

737 

8.7,5 

670 

1072 

402 

1340 

2144 

804 

9.00 

729 

1166 

437 

1458 

2333 

875 

9-25 

791 

1266 

475 

1583 

2533 

950 

9.50 

857 

1372 

514 

1715 

2744 

1029 

9-75 

927 

1483 

556 

1854 

2966 

ma 

10.  OO 

IOOO 

1600 

600 

2000 

3200 

1  200 

382 


TKAfirSMISSIOAT  OF  POWER. 


For  a  shaft  i  in.  diam.  greatest  distance  between  bearings  1 2.6ft. 


2 

3 

4 
•5 
6 

7 
8 

9 

10 
1 1 


16 
18 

20 
22 
23 
24 

25 
26 

27 
28 


'    12  29       " 

Telodynamic  or  Wire-rope  Transmission.— When  we  con- 
sider that  a  4-inch  line  of  shafting  transmitting  200  horse-po\ver 
at  200  revolutions  per  minute  would  require,  with  its  couplings, 
some  50  pounds  of  metal  per  linear  foot,  exclusive  of  the  bear- 
ings, while  the  same  power  could  be  transmitted  by  a  wire  rope- 
weighing  not  more  than  \\  pounds  per  foot,  we  realize  the 
immense  advantage  of  the  latter  mode  of  transmission  where 
applicable.  Wire  rope  for  transmission  is  made  of  steel  or 
wrought-iron  wire  twisted  into  strands,  which  in  turn  are  twisted 
around  a  hemp  centre  to  form  a  rope.  The  hemp  centre 
makes  the  rope  more  flexible  and  diminishes  the  internal  wear. 
The  flexibility  is  also  greater  as  the  number  of  wires  is  greater 
and  their  diameter  less.  The  common  American  practice  is 
to  put  19  wires  in  a  strand  and  6  strands 
in  a  rope,  Fig.  189.  Some  makers  put 
a  hempen  core  in  each  strand,  but  this  is 
not  the  common  practice.  The  twist  of 
the  rope  is  usually  in  the  opposite  direc- 
tion to  that  of  the  separate  strands.  One 
important  application  of  wire-rope  trans- 
mission is  in  the  cables*  of  street  railways, 
and  these  are  said  to  last  longer  and  wear 


FIG.  189. 


*  See  Fairchild  on  Street  Railroads,  1892,  p.  102. 


WIRE  ROPE. 


383 


better  when  the  twist  of  the  rope  is  in  the  same  direction  as 
that  of  the  strands. 

Wire  rope  running  on  a  pulley  and  enveloping  one-half  the 
circumference  undergoes  a  contraction  of  the  inner  wires  and 
an  extension  of  the  outer.  For  the  part  in  contact  with  the 
pulley,  the  outer  wires  exceed  the  inner  by  about  i£  times  the 
diameter  of  the  rope.  In  a  12-foot  pulley  this  difference  is 
distributed  over  about  19  feet  of  rope.  In  a  24-inch  pulley  it 
takes  place  in  a  length  of  about  3  feet,  and  the  buckling  of  the 
inner  fibres  and  stretching  of  the  outer  lead  to  a  very  rapid 
destruction  of  the  rope.  On  this  account,  the  pulleys  for  wire- 
rope  transmission  should  be  as  large  as  practicable.  Diameters 
of  1 2  to  15  feet  are  usually  adopted ;  smaller  sizes  can  be  used 
when  other  considerations  control,  but  the  smaller  the  size  the 
more  rapid  is  the  deterioration  of  the  rope. 

TABLE  7.— CRUCIBLE-STEEL  WIRE  ROPE,  6  STRANDS. 
19  WIRES  PER  STRAND.  HEMP  CENTRE. 


Diameter  in 
Inches. 

Breaking 
Strain  in 
Tons  of  2000 
Pounds. 

Working 
Load  in  Tons 
of  2000 
Pounds. 

Weight  per 
100  Feet, 
Pounds. 

1 

4-5 

0-75 

26 

o-5 

7-5 

I 

35 

0.62 

14 

2 

63 

0.75 

18 

3 

88 

0.87 

25 

5 

120 

i 

33 

6 

158 

I.  12 

42 

8 

200 

1.25 

52 

10 

250 

i-37 

63 

ii 

300 

1.50 

77 

12 

365 

The  Velocity  of  Wire  Rope  is  of  course  limited  by  the  con- 
sideration that  no  dangerous  strain  shall  occur  in  the  rim  of  the 
pulley.  This,  however,  is  of  but  slight  importance,  because. 
long  before  the  velocity  reaches  a  point  that  can  set  up  any 
dangerous  strain  in  the  rim,  the  centrifugal  force  in  that  part 
of  the  rope  which  is  in  contact  with  the  pulley  so  loosens  the 
grip  of  the  rope  that  it  slips.  In  a  15 -foot  pulley  with  its  rim 


384 


TRANSMISSION  OF  POWER. 


running  100  feet  per  second,  each  pound  of  the  rim  would  tend 
to  fly  off  radially  with  a  force  of  41.66  pounds,  which  would 
occasion  a  bursting  strain  in  the  material  of  about  1041  pounds 
per  square  inch — a  matter  of  no  consequence.  The  centrifugal 
force  acting  upon  the  rope,  assuming  the  latter  to  weigh 
i  pound  per  foot,  diminishes  its  pressure  upon  the  pulley  by 
nearly  1000  pounds,  and  to  that  extent  diminishes  its  adhesion 
to  the  pulley  and  the  power  that  can  be  transmitted  by  it. 
The  centrifugal  force  not  only  diminishes  the  pressure  of  the 
rope  on  the  pulley,  but  diminishes  the  arc  of  the  pulley 


FIG.  190. 


FIG.  191. 


embraced  by  the  rope.  For  these  reasons  100  feet  per  second 
is  thought  to  be  the  extreme  limit  of  the  velocity,  and  in 
practice  it  is  usually  put  considerably  below  that  figure,  often 
not  more  than  75. 

Fig.  192  shows  the  general  arrangement  of  turbines  on 
vertical  shafts  for  a  system  of  wire-rope  transmission.  The 
turbines  are  set  Avith  their  centres  in  the  same  straight  line,  and 
give  motion,  by  means  of  bevel-gears,  to  a  horizontal  shaft 


WIRE  ROPE. 


385 


elevated  so  that  the  rope  will  clear  the  ground  and  intervening 
objects.  As  many  wheels  and  as  m!my  pulleys  can  be  used 
as  the  extent  of  the  development  calls  for,  and  pulleys  can  be 
placed  on  each  end  of  the  line  of  shafting  if  desired.  A  trans- 
mission-line sometimes  consists  of  a  single  rope  reaching  the 


FIG.  192. 

entire  distance  and  resting  on  intermediate  carrier-pulleys. 
This  arrangement  is  unavoidable  in  street-railway  cables. 
The  best  practice  consists  in  dividing  the  distance  into  a  num- 
ber of  spans  and  using  a  separate  rope  for  each  span  with 
pulleys,  as  indicated  by  Fig.  191.  The  rim  of  this  pulley  has 
two  grooves,  one  for  the  incoming  and  one  for  the  outgoing 
rope.  Fig.  190  is  a  section  of  the  rim  of  a  pulley  for  a  single 
rope,  such  as  would  be  used  to  deliver  power  from  a  shaft  to  a 
rope,  or  to  drive  a  shaft  by  means  of  a  rope.  The  bottom  of 
the  groove  in  which  the  rope  runs  is  deeply  widened  into  a 
channel  of  trapezoidal  cross-section  reaching  around  the  pulley. 


386 


TRANSMISSION  OF  POWER. 


This  channel  is  packed  solidly  with  pieces  of  leather  inserted 
radially  and  presentinf  their  edges  to  the  rope.      This  con- 


FIG.  193. 


FIG. 

struction  is  found  very  conducive  to  the  preservation  of  the 
rope.  The  line  pulleys  are  placed  on  towers  or  trestles 
elevated  above  the  general  level  of 
the  ground.  The  pulley,  Fig.  191, 
can  only  deliver  power  in  the  same 
line  as  it  is  received.  When  it  is 
necessary  to  change  the  direction  of 
the  rope  the  disposition  of  Fig.  194 
is  used,  in  which  the  shafts  of  the 
pulleys  are  connected  by  bevel-gears, 
made  to  an  angle  equal  to  the  angle 
of  deviation  of  the  line,  i.e.,  the 
angle  between  the  pitch-circles  of  the  gears  is  equal  to  the 
angle  of  deviation. 

The  Horizontal  Turbine,  placed  above  tail-water  and  dis- 
charging through  a  draft-tube,  lends  itself,  under  certain  limita- 
tions, very  readily  to  wire-rope  transmission. 


FIG.  194. 


WIRE  ROPE. 


387 


In  the  arrangement  of  Fig.  153  it  is  obvious  that  a  wire- 
rope  pulley  might  be  applied  to  either  end  of  the  horizontal 
shaft,  or  one  to  each  end. 

There  is  no  insuperable  mechanical  difficulty  in  driving  a 
rope  directly  from  a  vertical  shaft,  although  the  arrangement 
is  somewhat  complex,  as  appears  from  Figs.  195  and  196. 


FIG.  195. 


FIG.  195^. 


FIG.  196. 

The  wire-rope  pulley  A  is  fixed  upon  the  head  of  the  water- 
wheel  shaft,  receiving  and  delivering  the  rope  horizontally. 
The  rope  envelops  considerably  more  than  half  the  circumfer- 
ence of  the  pulley,  so  that  the  two  plies  come  into  the  same 
vertical  plane  at  a  short  distance  therefrom.  Here  each  of  the 
two  plies  passes  a  pulley  on  a  horizontal  axis  B  and  C  and 
takes  a  vertical  direction.  At  a  sufficient  elevation,  the  two 


388  TRANSMISSION  OF  POWER. 

plies  again  change  direction  by  the  two  pulleys  D  and  E  which 
run  in  the  same  vertical  plane,  and  thence  the  rope  runs  hori- 
zontally, forming  a  part  of  the  main  line.  It  is  manifest  that 
the  pulley  E  could  be  left  out  of  the  system,  the  two  plies  d 
and  e  passing  over  the  pulley  D  and  the  rope  which  envelops 
the  four  pulleys  A,  B,  C,  and  D,  forming  a  complete  circuit. 
D  in  that  case  is  a  double  pulley  of  the  form  indicated  at  Fig. 
191,  and  sends  off  another  rope,^,  Fig.  195*7,  to  the  main  line. 
Power  Transmissible  by  Wire  Rope.  —  If  tl  =  the  tension 
•on  the  tight  ply  of  the  rope,  and  /2  on  the  loose  ply,  v  being 
the  velocity  in  feet  per  second,  tv  and  /2  being  expressed  in 
pounds,  the  power  P  in  horse-power  is 


Let  r  =  the  radius  of  the  pulley,  s  the  length  of  rope  in 
contact  with  the  pulley,  and  /"the  coefficient  of  friction  between 
the  rope  and  pulley  ;  then  when  the  rope  is  ready  to  slip  on  the 
pulley 

tl  =  tax  (2.718)7'  .....      (60) 

It  is  seldom  necessary  to  consider  any  other  case  than  that 
in  which  the  two  plies  of  the  rope  are  substantially  parallel,  and 

in  that  case  -   =  n  —  3.14.      The  coefficient  f,  between  iron 

and  leather,  where  no  unguent  is  used,  may  be  taken  at  0.31 
to  o.  34.  Where  the  surfaces  are  fully  lubricated  it  will  not 
exceed  0.14.  It  is  conducive  to  the  durability  of  wire  ropes 
to  keep  the  hempen  core  saturated  with  oil,  and  in  hoisting- 
ropes,  which  run  on  small  pulleys,  this  lubrication  cannot  be 
dispensed  with.  This  necessity  diminishes  as  the  diameters  of 
the  pulleys  are  greater.  In  pulleys  of  the  size  contemplated 
here,  we  may,  most  commonly,  regard  the  exterior  of  the  rope 

as  dry.      Adopting  /=  0.3,  we  have  —  /=  0.94,  and  for  the 


TENSION  AND   DEFLECTION.  389 

extreme  value  of  ^  we  may  put  /x  =  2.56/2.  On  the  other 
hand,  if  we  regard  the  surfaces  as  fully  lubricated,  f=  0.14, 

-/==  0.44,  and  ^  =  i.55*2. 

Tension  and  Deflection. — A  rope  or  chain  suspended  from 
two  fixed  points  and  hanging  freely  under  the  action  of  gravity 
assumes  a  curve  called  the  catenary,  whose  equation,  referred 
to  horizontal  and  vertical  lines  passing  through  its  lowest 
point,  is 

y  =\l\E~' -  E~~^     ,       .      .      .      .      (61) 

in  which  x  and  y  are  the  coordinates  of  the  curve,  I  =  a  length 
of  the  rope  equal  in  weight  to  the  horizontal  tension  on  the 
lowest  point  of  the  curve,  E  =  the  base  of  the  Naperian  system 
of  logarithms  —  2.7183. 

When  x  =  a  =  the  half-span,  y  represents  the  deflection 
or  sag  of  the  rope. 

Also,  if  s  represent  the  half-length  of  the  rope, 

S  =  ^I(ET-E~J) (62) 

Table  8  will  be  found  useful  in  any  calculations  relative  to 
the  deflection,  tension,  or  length  of  wire  ropes  used  in  trans- 
mission. It  contains  the  values  of  the  quantity  within  the 

Cl  ^C 

parenthesis  for  all  practical  values  of  j  or  --..      Suppose,  for 

instance,  it  be  required  to  find  the  sag  of  a  rope  weighing  1.2 
pounds  per  linear  foot,  with  a  span  of  600  feet  and  a  tension  of 

6000 
6000  pounds  on  the  lowest  point.      Here  /=  =  5000  ft., 

a  =  300,  —.  =  .03.  Looking  in  col.  5  of  the  table,  opposite 
0.030  in  col.  i  we  find  0.0036,  which  is  the  value  of 

\E2t  —  E  2/;  in  eq.  (61).  This  multiplied  by  \l  gives  y  = 
2500  X  .0036  =  9.00. 

*  See  Moseley's  Mechanics,  1866,  p.  506. 


390  TRANSMISSION  OF  POWER. 

TABLE   8.— TENSION    AND    DEFLECTION    OF   WIRE    ROPE. 


I 

j 

3 

4 

5 

a      x 

a 

a 

a        a 

1   °f   27' 

E~l  . 

El  -  E~~t  . 

(£7-£-l)* 

0.005 

.O050I 

0.99501 

O.OIOOO 

O.OOOIO 

O.OIO 

.OIOO5 

0.99005 

0  .  02000 

0.00040 

0.015 

.OI5II 

0.98511 

0.03OOO 

0.00090 

O.O20 

.  0202O 

0.98020 

O.O4000 

0.00160 

0.025 

.02530 

0-97531 

O.O5OOO 

0.00250 

O.O3O 

•03045 

0.97045 

O.O6OOO 

0.00360 

0.035 

.03562 

0.96561 

O.O700I 

0.00490 

O.040 

.04081 

0.96079 

0.08002 

o  .  00640 

0.045 

.04603 

0.95600 

o  .  09003 

0.00811 

O.05O 

.05127 

0.95123 

0.10004 

O.OIOOI 

0-055 

.0565 

0.9464 

O.IIOI 

O.OI2I 

O.O6O 

.O6l8 

0.9418 

0  .  I  200 

0.0144 

O.005 

.0671 

0.9371 

0.1300 

0.0169 

O.O7O 

.0725 

0.9324 

o.  1401 

0.0196 

0.075 

.0779 

0-9275 

0.1504 

0.0226 

0.080 

•0833 

0.9231 

o.  1602 

0.0257 

o  085 

.0887 

0.9185 

0.1702  . 

0.0290 

0.090 

.0942 

0.9139 

0.1803 

0.0325 

0.095 

.0997 

0.9094 

0.1903 

0.0362 

O.IOO 

.1051 

0.9048 

0.2003 

0.0401 

0.105 

.IIO7 

0.9003 

0.2104 

0.0443 

O.IIO 

•Il63 

0.8958 

0.2205 

0.0486 

0.115 

.1219 

0.8914 

0.2305 

0.0531 

0.120 

•1275 

0.8869 

0.2406 

0.0578 

0.125 

•1331 

0.8825 

o  2506 

0.0628 

O.I3O 

.1388 

0.8781 

0.2607 

0.0680 

0-135 

•1445 

0-8737 

0.2708 

0.0733 

•1503 

o  .  8694 

0.2809 

0.0789 

0.145 

.  1560 

0.8650 

o.  2910 

0.0847 

O.I5O 

.I6l8 

0.8607 

0.3011 

0.0911 

0.155 

.1677 

0.8564 

0.3113 

o  .  0969 

0.160 

•1735 

0.8521 

0.3214 

0.1033 

0.165 

.1794 

0.8479 

0.3315 

0.1099 

0.170 

•1853 

0.8437 

0.3416 

0.1167 

0.175 

1912 

0.8395 

0.3517 

o.  1227 

o.i  So 

.1972 

0.8353 

0.3619 

0.1310 

0.185 

.2032 

o  8311 

0.3721 

0.1384 

0-190 

.2092 

0.8270 

0.3822 

o  1461 

0.195 

•2153 

0.8228 

0.3925 

0.1541 

O  20O 

.2214 

0.8187 

0.4027 

o.  1622 

0-205 

•2275 

0.8146 

0.4129 

0.1705 

O.2IO 

•2337 

0.8106 

-0.4231 

0.1790 

0.215 

•2399 

0.8066 

0.4333 

o.  1877 

O.22O 

.2461 

0.8025 

0.4436 

0.1968 

O.225 

.2523 

0.7985 

0.4538 

0.2059 

0.23O 

.2583 

0-7945 

0.4641 

0.2154 

0-235 

.2649 

o.  7906 

0.4743 

0.2250 

O.24O 

•2713 

0.7866 

0.4847 

0.2349 

0.245 

.2776 

0.7827 

0.4949 

0.2449 

0.250 

.2840 

0.7788 

0.5052 

0.2552 

TENSION  AND   DEFLECTION.  391 

Suppose  we  wish  to  transmit  400  horse-power  by  a  rope  of 
the  above  weight  connecting  two  1  5-foot  pulleys,  540  feet 
centre  to  centre,  running  80  feet  per  second,  and  suppose  both 
plies  of  the  rope  to  be  under  a  tension  of  31  80  pounds  when 
not  running.  To  find  the  sag. 

When  not  running 

3180  a          270 

/=:—-=  2650,     _,-  =   _  =  0.05  I, 

for  which  col.  5  gives  .01043,  and  we  have 

2650 
y  =  —  X  .01043=  14-  34  ft. 

When  the  rope  is  running  we  have 


whence  ^  =  4555,     ^  =  1805. 

For  the  tight  side 

/  =  379<5,     ^  =  .0356, 

from  which  we  find 

y  —  1898  X  .00508  =  9.64, 
And  for  the  loose  side 

7=1504,      ^  =  0.0897,     ^=752x0.0322  =  24.21. 

To  find  the  total  length  of  the  rope,  consider  it  when  not 
running.     -.  =0.102,  for  which  col.  4  gives  0.2043,  an<3  by 

eq.  (62)  2s  =  one  ply  =  2650  X  0.2043  =  ........      541-H 

For  the  other  ply  ..............................     54I-H 

One  entire  circumference  =  ......................       47-12 

Total  length  of  rope  ......................    1129.40 


392  TRANSMISSION  OF  POWER. 

The  length  of  the  rope  does  not  change  when  running ;  for 
though  the  tight  side  stretches  slightly  under  the  increased 
tension,  the  loose  side  contracts  to  substantially  the  same 
extent  under  the  diminished  tension. 

There  is  an  advantage  in  making  the  lower  ply  of  the  rope 
the  tight  side,  as  we  can  then  reckon  the  sag  of  the  loose  side 
from  the  top  of  the  pulleys.  This  arrangement  has  another 
slight  advantage  in  that  the  rope  envelops  a  trifle  more  than 
half  the  circumference  of  the  pulley,  whereas,  with  the  loose 
ply  below,  it  envelops  a  trifle  less  than  half.  The  practical 
limit  to  the  length  of  span  that  can  be  employed,  subject  to 
this  method,  is  the  condition  that  the  loose  ply  shall  not  sag 
below  the  tight  one  and  occasion  mutual  injury  by  chafing. 
The  above  supposition  of  a  span  of  540  feet  comes  sufficiently 
near  to  this  limit,  as  the  loose  ply  would  hang  24.21  feet  below 
the  top  of  the  pulleys,  and  the  tight  one  15  -f  9.64  =  24.64. 
It  would  no  doubt  be  practicable  to  run  a  rope  on  pulleys  a 
thousand  feet  apart,  but,  in  that  case,  the  loose  ply  would  have 
a  sag  of  more  than  60  feet,  and  this  must  be  reckoned  from  the 
lowest  point  of  the  pulley,  as  otherwise  the  loose  ply  would 
hang  far  below  the  tight  ply. 

The  critical  reader  will  notice  that  these  results,  though 
sufficiently  accurate  for  any  practical  purpose,  are  not  consis- 
tent with  strict  mathematical  nicety,  as  we  assume  the  upper 
ply  to  hang  from  the  highest  point  of  the  pulley,  and  the  lower 
ply  from  the  lowest.  This  is  not  strictly  correct,  owing  to  the 
slight  inclination  of  the  rope.  It  would  be  easy  to  correct  this 
trifling  error  if  it  were  worth  while. 

Case  of  One  Pulley  Higher  than  the  Other. — The  fore- 
going assumes  that  both  pulleys  are  on  the  same  level,  in  which 
case  the  relations  of  sag  and  tension  are  comparatively  simple  ; 
but  these  methods  become  inapplicable  when,  as  most  com- 
monly occurs,  the  two  pulleys  are  not  in  the  same  horizontal 
line.  In  this  case  we  must  regard  the  curve  as  forming  a  part 
of  a  more  extended  catenary  whose  suspension  points  are  on 
the  same  level,  viz.,  the  level  of  the  higher  point.  In  Fig. 


CASE   OF  ONE  PULLEY  HIGHER    THAN   THE   OTHER.     393 


197,  rt'and  e  are  two  pulleys  at  different  elevations,  connected 
by  a  wire  rope  with  lower  side  tight.  This  side  is  to  be 
regarded  as  a  part  of  the  catenary  ACB,  and  the  elements  of 
this  catenary  are  to  be  arrived  at  by  a  laborious  process  of  trial 
and  error.  We  will  state  without  demonstration  some  proper- 
ties of  the  curve,  referring  the  reader  who  is  desirous  of  fuller 
information  to  the  discussion  of  the  catenary  in  treatises  on  the 
calculus.  Let  CH  be  a  horizontal  line  through  the  lowest 
point  of  the  catenary  ;  let  x  and  y  be  the  coordinates  of  any 
point  r  of  the  curve.  When  x  =  a,  the  semispan,  y  =  /i,  the 


FIG.  197. 


sag  of  the  rope.  At  the  point  r,  if  a  tangent  be  drawn  to  the 
curve,  it  forms  with  the  horizontal  and  vertical  through  C  a 
triangle  such  that  if  6y~be  taken  to  represent  the  tension  on 
the  lowest  part  of  the  curve,  fk  will  represent  the  tension  at  r, 
and  Ck  the  weight  of  the  rope  Cr.  Expressing  these  several 
tensions  in  equivalent  lengths  of  rope,  we  put  /()  for  the  tension 
at  C ',  /!  for  that  at  r,  and  /2  for  that  at  B.  The  quantity  in 

column  4  of  the  table,  corresponding  to  -j-  in  the  first,  is  twice 

19 

the  tangent  of  the  angle  Cfk.  As  a  basis  of  computation, 
suppose  the  pulleys  to  be  300  feet  apart  horizontally,  50  feet 
vertically.  We  know  within  narrow  limits  what  tension  /,  we 


394  TRANSMISSION  OF  POWER. 

require  at  r,  say  /t  =  3600.  We  know  that  l(>  is  but  little  less 
than  /,,  say  /0  =  3480.  To  find  a  we  proceed  thus:  Assume 
a  value  of  a,  and  find  by  equation  (61)  the  corresponding  value 
of//.  Thus  a  —  300  =  x,  h  —  50  —  y.  See  if  these  values 
will  satisfy  equation  (61).  If  not,  amend  the  supposition  and 
try  again. 

First,  take  a  =  700.      -      =  >~-  =  o.  1006.      Find  in  the 


fifth  column  of  the  table  the  quantity  corresponding  to  o.  1006 
in   col.    i,   viz.,   0.0406.      Then  h  =  1740  X  .0406  =  70.64. 
.  •.     x  —  700  —  300  =  400,      '  y  =  70.64  —  50  =  20.64. 
To  compute^: 
x         400 
17  ^  6960"  •°575'       •'•    -^  -OI325  X  1740  =  23.05. 

This    shows    that    we    have    not   taken    a   large    enough. 
A  larger   value  of  a  would  give  a  larger  value  of  //  and   a 

relatively  smaller  value  of  y.  Take  a  =  725.  —  r  —  0.1042, 
//  =  1740  X  -0436  =  75.86.  Whence  x  =  425,  y  =  25.86, 

—r=  .061,  y=  1740  x  -OH93  =25.98.      This   agreement    is 

2/o 

sufficiently  close  and  shows  that  a  catenary  of  1450  feet  span 

and  a  tension  of  /0  =  3480  at  the  lowest  point  will  go  through 
the  centres  of  the  pulleys.  We  want  it,  however,  merely  to 
touch  the  circumference  of  the  pulleys.  Call  A  the  angle 
which  a  tangent  to  the  curve  makes  with  the  horizontal. 
Then  for  x  =  425  and  y  =  25.86  we  have 


-  0.1211. 

/o          3480 


The  quantity  in  the  fourth  column  of  the  table  corresponding 
to  0.12 1 1  in  the  first,  {50.2428,  and  o.  1214  is  the  tangent  of  A 
for  r  —  tangent  cfk.  .-.  cfk  =  6^  54'.  In  like  manner  CmE 
=  11°  48'.  Therefore  for  the  practically  correct  value  of  /u  we 


THE   EFFICIENCY   OF   WIRE- ROPE    TRANSMISSION.     395 
have  /„  =  3600  cos  6°  54'  =  3574,  expressed  in  feet  of  rope. 

And  for  the  tension  at  B  we  have  /.,  = -0— 

cos  1 1    48 

We  can  now  correct  the  horizontal  and  vertical  distances 
of  the  points  of  suspension.  Call  R  the  radius  of  the  pulley; 
the  radius  through  the  point  of  tangency  of  the  rope  makes 
an  angle  A  with  the  vertical  through  the  centre.  The  hori- 
zontal distance  of  these  tangent  points  is 

300  -f  R  sin  1 1°  48'  —  R  sin  6°  54', 
and  the  vertical  distance 

50  +  R  cos  6°  54'  —  R  cos  1 1°  48'. 

With  these  revised  values  we  repeat  the  trial  and  error  process 
and  find  a  with  sufficient  accuracy.  The  same  process  can  be 
applied  to  the  upper  ply  of  the  rope  if  desired.  The  main 
object  of  these  computations  is  to  obtain  the  required  differ- 
ence of  tension  without  too  great  a  strain  on  the  axis  of  the 
pulley  and  without  so  great  a  sag  in  the  loose  ply  as  will 
allow  it  to  interfere  with  the  tight  one.  Much  information  as 
to  existing  wire-rope  installations  is  contained  in  Mr.  W.  C. 
Unwin's  book,  "Development  and  Transmission  of  Power," 
London,  1894. 

The  Efficiency  of  Wire-rope  Transmission  for  short  dis- 
tances is  probably  greater  than  for  any  other  mode.  The 
principal  losses  are  the  friction  of  the  pulleys  on  their  journals 
and  the  bending  of  the  rope,  which  latter  loss  diminishes 
greatly  as  the  diameter  of  the  pulley  increases.  For  the  end 
pulleys  of  a  transmission  system  the  tension  of  the  rope  acts 
on  the  journals,  but  the  intermediate  pulleys  bring  no  pressure 
on  their  journals  but  their  own  weight  and  the  weight  of  the 
rope.  It  is  the  disadvantage  of  the  system  that  these  losses 
are  the  same  whether  the  power  transmitted  be  great  or  small. 

Zeigler,  at  Oberursel,  found  a  loss. of  13.5  per  cent  in  a  line 
of  seven  spans  carrying  104  h.p.  at  the  sending  end.  This 
would  indicate  a  loss  of  2  per  cent  in  each  span ;  that  is  to  say, 


39  7'£ANSMlSSWAr   OF  POWER. 

the  power  received  at  any  station  is  98  per  cent  of  that  trans- 
mitted from  the  next  preceding  station.  According  to  this,  at 
the  end  of  a  mile,  allowing  ten  stations  of  528  feet  each,  the 
efficiency  would  be  o.gS10  =  0.817,  and  at  the  end  of  2  miles 
o.QS20  =  0.668.  At  half-load  the  relative  loss  would  be  twice 
as  great.  The  efficiency  in  one  span  would  be  0.96;  at  the 
end  of  a  mile  0.664,  2  miles  0.442.  Wire  rope,  though  not 
suitable  for  long  distances,  has  advantages  for  distances 
between  100  yards  and  I  mile  not  possessed  by  any  other 
method,  especially  as  the  power  does  not  require  to  be  changed 
into  any  other  form  of  energy  before  transmission. 


CHAPTER    XIX. 
HYDRAULIC   TRANSMISSION. 

THE  use  of  water  under  high  pressure  very  naturally  sug- 
gests itself  as  a  means  of  transmitting  energy  to  distant  points. 
Pipes  buried  underground  are  preferable  on  many  accounts  to 
towers,  ropes,  and  their  accessories,  especially  in  populous  dis- 
tricts. Systems  of  water-distribution  for  domestic  purposes 
often  involve  arrangements  for  the  use  of  the  water  for  power. 
The  difficulties  met  with  in  this  application  are:  (i)  Under  the 
moderate  pressure  required  for  domestic  uses,  seldom  exceed- 
ing 200  feet,  or  86.5  pounds  on  a  square  inch,  a  comparatively 
large  quantity  of  water  is  required,  and  as  this  must  all  be  of  the 
quality  required  for  domestic  consumption,  which  costs  some-- 
thing for  collection,  purification,  and  storage,  the  water  itself 
is  expensive.  (2)  The  points  where  power  is  required  are 
commonly  much  higher  than  the  source  from  which  it  is 
pumped  or  the  watercourse  to  which  it  returns  after  use ;  so 
that  a  large  percentage  of  the  power  represented  by  the  water 
is  wasted.  In  a  city  like  Chicago,  which  has  the  inexhaustible 
volume  of  Lake  Michigan  to  draw  from  and  lies  on  a  level 
plain  only  a  few  feet  above  the  lake-surface,  these  difficulties 
do  not  appear,  and  it  is  accordingly  not  strange  that  large 
amounts  of  power  are  drawn  from  the  mains  of  this  city 
especially  for  operating  passenger-elevators.  The  above  objec- 
tions, however,  are  so  serious,  in  the  ordinary  case,  that  the 
plan  of  combining  domestic  water-supply  with  power-distribu- 
tion, though  it  once  looked  inviting  and  had  zealous  advocates, 
has  never  met  with  extended  application.  Where  the  latter 

397 


398  HYDRAULIC   TRANSMISSION. 

has  been  applied,  it  has  usually  been  by  a  separate  system  of 
pipes,  and  under  pressures  greatly  in  excess  of  those  required 
for  domestic  uses. 

This  mode  of  transmission  was  first  applied  to  the  operation 
of  cranes  and  lifts  in  the  docks  and  warehouses  of  London, 
where  the  only  mechanical  movement  required  was  the  hauling 
in  and  letting  out  of  a  rope.  This  was  accomplished  by  means 
of  a  piston  -moving  in  a  cylinder  and  carrying  a  series  of  pulleys 
or  sheaves  attached  to  the  free  end  of  the  piston-rod.  Around 
these  pulleys  and  a  contiguous  series  of  fixed  pulleys  the  rope 
or  chain  was  rove,  so  that  a  small  movement  of  the  piston 
caused  a  great  movement  of  the  rope  or  chain.  The  unavoid- 
ably intermittent  operation  of  these  machines  necessitated 
means  for  storing  the  energy  of  the  motor  during  those  times 
when  no  demands  were  made  on  it.  A  reservoir  was  out  of 
the  question  because  in  such  situations  no  sufficient  height 
could  be  obtained.  An  air-chamber  is  inadmissible  for  the 
reason,  first,  that  it  would  deliver  the  water  at  a  varying  pres- 
sure, and,  second,  because  water  at  such  high  pressures 
speedily  absorbs  the  air  and  necessitates  special  means  for  its 
renewal.  Out  of  these  conditions  grew  the 

Accumulator,  which  is  a  large  cylinder  with  an  enormously 
heavy  plunger.  The  surplus  water  not  required  by  the 
machines  passes  into  this  cylinder,  raises  the  plunger,  and 
forms  a  reserve  of  power  to  be  drawn  when  the  demand  of  the 
machines  exceeds  the  capacity  of  the  motor.  The  absolute 
amount  of  power  stored  in  this  fixture  is  very  small,  not  often 
more  than  one  horse-power  for  a  couple  of  hours,  but  it  serves 
a  very  useful  purpose  in  regulating  the  system.  Of  course 
when  a  reservoir  at  a  sufficient  height  is  obtainable  it  is  to  be 
preferred.  Such  a  system,  which  hardly  ever  commands  a  head 
of  more  than  500  feet  or  a  pressure  of,  say,  220  pounds  per 
square  inch,  may  for  distinction  be  called  a  low-pressure  sys- 
tem, while  a  system  of  hydraulic  transmission  involving  the 
use  of  accumulators,  where  the  pressure  is  usually  700  or  800 
pounds  per  square  inch,  may  be  called  a  higk-pressure  system. 


LOSS  OF  HEAD    IN  PIPES. 


399 


Mr.  Unwin  gives  the  following  table  of  the  gross  horse- 
power transmissible  by  different  mains  at  a  velocity  of  3  feet 
per  second: 

GROSS  H.P.   TRANSMITTED    BY    DIFFERENT  MAINS. 


Low-pressure  System, 
Head  500  Feet. 

High-pressure  System, 
750  Pounds  per  Square  Inch. 

Diameter  of 
Main  in  Inches. 

Gross  H.P. 
Transmitted. 

Diameter  of 
Main  in  Inches. 

Gross  H.P. 
Transmitted. 

9 

75 

3 

29 

12 

133 

6 

116 

iS 

300 

9 

260 

24 

533 

12 

463 

Loss  of  Head  in  Pipes.  —  In  a  mile  of  6-inch  pipe  with  a 
velocity  of  3  feet  per  second  the  loss  of  pressure  will  be  some 
1  5  pounds  per  square  inch  when  new,  and  this  will  be  increased 
to  31  when  the  pipe  is  rusted  and  covered  with  incrustations, 
as  it  usually  is  after  the  lapse  of  time.  The  following  formula 
is  convenient  for  application  to  pipes  of  6  inches  diameter  and 
under: 


/  being  the  length  in  feet,  q  the  quantity  of  water  flowing  in 
cubic  feet  per  second,  d  the  diameter  in  inches,  and  h  the  loss 
of  pressure  represented  by  feet  of  head.  Mr.  Unwin  gives  the 
formula 


in   which  h  and   /  are  as  before,   d  =  diameter  in  feet,  v  = 
velocity  in   feet   per   second,  and  k  =  a  coefficient  which  for 
d  =  o.  5  may  be  taken  as  0.000375. 
For  d  =?  I  ,     k  —  o.  000344. 
«  2      "      0.000312. 


400 


HYDRAULIC    TRANSMISSION. 


The   following  tables   are  also   taken   from   Mr.    Unwin's 
book: 


Diameter  of 
Main  in 
Inches. 

Loss  Due  to  Fr 

] 
ction  per  Mile. 

In  Feet  of  Head. 

In  Pounds  per  Sq.  In. 

Clean. 

Incrusted. 

Clean.           Incrusted. 

6 
12 

35-5 
16.3 

70.9 

32-5 

15  37            30.70 
7.06            14.07 

24 

7-4 

I4.8 

3.20     |         6.41 

Diameter  of 
Main  in 
Inches 

Loss  per  Mile  in  Per  Cent  of  Total  Head. 

For  Pressures  in  Feet  of 

100 

250 

500 

1000 

1600 

6 

35-5 

14.2 

7-i 

3-5 

2.2 

12 

16.3 

6.6 

3-3 

1.6 

1.0 

24 

7-4 

2.8 

1.4 

0-7 

0-5 

The  above  is  for  new  and  clean  pipes.  For  pipes  fully 
incrusted  the  percentage  loss  will  be  twice  as  great.  This 
table  also  contemplates  a  velocity  of  3  feet  per  second.  It 
shows  clearly  the  great  advantage  of  high  pressures  in  a 
transmission  system.  With  such  pressures  as  are  usual  in 
water-supply  systems,  the  loss  of  head  in  a  mile  of  pipe 
amounts  to  a  very  material  percentage  of  the  entire  power ; 
but  \vhere  we  deal  with  pressures  of  700  or  800  pounds  per 
square  inch,  the  loss  cuts  so  small  a  figure  that  it  may,  in  pre- 
liminary computations,  be  neglected. 

Systems  of  hydraulic  distribution  for  general  industrial  pur- 
poses exist  in  London,  Liverpool,  Hull,  Birmingham,  and 
Manchester,  England ;  in  Antwerp,  Holland ;  and  in  many 


MOTORS.  401 

other  places.  The  installation  recently  completed  at  Man- 
chester is  understood  to  use  water  under  a  pressure  of  1600 
pounds  per  square  inch.  All  the  above-named  systems  de- 
rive their  power  primarily  from  steam,  and  do  not  directly 
concern  a  treatise  on  water-power. 

At  Zurich  in  Switzerland,  power  derived  from  a  small  fall 
in  the  river  Limmat  is  distributed  to  a  great  number  of  small 
industries  by  hydraulic  pressure.  Water  is  pumped  into  mains 
communicating  with  a  reservoir  some  6000  feet  from  the  pump- 
ing-station,  at  an  elevation  of  over  500  feet.  The  effective 
pressure  at  the  motors  is  475  feet,  and  the  distributing  mains 
have  an  aggregate  length  of  1 5  ooo  feet.  The  charge  to  con- 
sumers who  use  less  than  20000  h.p.  hours  per  annum  is  2.5 
cents  per  h.p.  hour.  To  those  who  use  50000  and  more, 
about  1.25  cents  per  h.p.  hour.  This  amounts  to  from  40  to 
80  dollars  per  horse-power  for  a  year  of  3000  working-hoi:rs. 

At  Geneva,  on  the  river  Rhone,  near  its  issue  from  Lake 
Leman,  is  a  considerable  amount  of  water-power,  transmitted 
and  distributed  by  hydraulic  pressure.  The  fall  here  varies 
from  12  feet  in  low  water  to  5.5  in  flood.  Turbines  are  used 
similar  to  the  Geyelin  wheel,  Fig.  148,  which  adapt  themselves 
to  the  varying  conditions  of  flow.  A  1 6-inch  main  leads  from 
the  pump-station  to  the  reservoir,  which  is  some  2^ .miles  dis- 
tant, at  an  elevation  of  390  feet  above  Lake  Leman,  with  some 
half  million  cubic  feet  capacity.  This  reservoir  is  of  great  im- 
portance to  the  system,  as  it  enables  the  water-wheels  to  run 
twenty-four  hours  a  day  and  store  up  their  energy  when  not 
wanted ;  whereas,  without  it,  they  could  only  run  during  the 
continuance  of  work,  and  would  run  at  considerable  disadvan- 
tage, being  obliged  to  pump  more  than  the  requirement  of  the 
motors  and  wasting  the  excess  through  a  relief-valve.  Previous 
to  the  construction  of  the  reservoir,  large  air-chambers  were 
use"d  to  regulate  the  pressure,  and  these  were  kept  charged 
with  air  by  a  compressor. 

The  Motors  originally  used  at  Geneva  were  ' '  Schmid  ' ' 
pressure-engines,  and  these  are  still  used  for  small  powers. 


402  HYDRAULIC   TRANSMISSION. 

They  use  a  quantity  of  water  which  depends  on  the  speed  only,, 
and  not  on  th  equantity  of  work  done ;  hence  are  uneconomical 
with  light  loads.  They  are  convenient  and  cheap,  can  be  run 
at  any  speed,  and  act  as  meters  of  the  quantity  of  water  used. 
A  counter  on  the  pressure-engine,  recording  the  number  of 
revolutions,  gives  the  means  of  ascertaining  accurately  the 
quantity  of  water  consumed.  At  full  load  their  efficiency  is  80 
per  cent. 

The  rotary  pressure-engine  is  not  necessarily  subject  to  the 
disadvantage  of  requiring  the  same  quantity  of  feed-water  for 
little  work  as  for  much.  A  device  can  be  introduced  whereby 
the  governor  acts  to  vary  the  position  of  the  crank-pin  accord- 
ing to  the  load,  so  that  for  a  light  load  the  traverse  of  the 
piston  and  consequent  consumption  of  water  is  small,  the 
piston  having  a  large  "  clearance  "  at  every  stroke.  This  large 
clearance  leads  to  no  waste  in  an  engine  worked  by  an  inelastic 
fluid,  though  it  would  be  ruinously  wasteful  in  a  steam-engine. 

For  all  large  motors,  at  Geneva,  impulse-turbines  are  used 
of  the  general  type  of  the  Pelton  wheel,  Figs.  149,  150.  These 
are  peculiarly  suitable  for  high  pressures,  and  give,  as  we 
have  seen,  page  304,  an  efficiency  fully  equal  to  the  best,  an 
efficiency  which  is  not  much  impaired  by  a  diminished  load. 
They  are  susceptible  of  close  regulation,  which  is  important  at 
Geneva,  the  industries  connected  with  watch-making  requiring 
uniform  speed. 

A  difficulty  occurs  here  which  is  inseparable  from  any 
system  having  a  reservoir  at  a  considerable  distance  from  the 
pumps  and  not  in  line  with  the  supply-pipe.  Water  flows 
toward  the  reservoir  while  the  delivery  of  the  pumps  exceeds 
the  consumption,  and  from  the  reservoir  to  the  supply-main.s 
in  the  contrary  case.  The  result  is  that  the  water  is  delivered 
to  the  small  motors  at  an  excessive  pressure  in  the  former  case, 
and  a  deficient  pressure  in  the  latter,  the  difference  being  the 
loss  of  head  in  5  miles  of  main,  with  a  flow  of  water  represent- 
ing the  excess  or  deficiency  of  the  pumpage.  Such  variations 
are  inadmissible  here,  because  the  water  is  paid  for,  not  by 


PIPES.  403 

meter  measurement,  but  by  computation  based  on  the  orifices 
of  discharge,  which  assumes  a  constant  pressure.  This  diffi- 
culty is  met  by  a  centrifugal  pump  actuated  by  a  separate 
motor,  which  expends  a  part  of  the  water  passing  the  main  in 
increasing  the  pressure  of  the  remainder  —  a  wasteful  device, 
but  necessitated  by  the  conditions  of  the  case. 

The  Pipes  for  a  pressure  system  require  greater  strength 
than  ordinary  water-pipes,  and  the  joints  require  more  attention, 
as  a  small  leak  under  such  great  pressure  represents  a  large 
loss  of  power.  The  tensile  strain  per  running  inch  on  one  side 
of  the  pipe  is  represented  by  \PD,  P  being  the  pressure  per 
square  inch,  and  D  the  diameter  in  inches.  Thus,  for  a  pressure 
of  750  pounds  per  square  inch  and  a  diameter  of  8  inches  the 
tensile  strain  is  4  X  7S°  =  3°°°  pounds  per  running  inch, 
-and  if  we  assume  cast  iron  with  a  safe  tensile  strength  of  6000 
pounds  per  square  inch,  this  would  require  the  pipes  to  be 
%  inch  thick.  They  are  usually  made  considerably  thicker  than 
this  consideration  would  dictate.  The  following  rule  or  some- 
thing very  similar  is  usually  applied,  /  being  the  thickness  in 
inches: 

/  =  .oooi?8DP  +  J. 

for  P  —  750  and  D  =  4  this  gives  /  =  0.78  inch,  say  |  inch. 
«     5     «<        «        «   j  05      «        «    T     « 

«  s  "    "    "  1.32  "    "  ij  " 

"   10     "       "       "   1.57     "       "    i  ^  " 


For  such  pressures  the  pipes  are  put  together  with  flanged 
joints  and  bolts,  a  ring  of  gutta  percha  or  lead  being  interposed 
between  the  abutting  surfaces.  For  pressures  up  to  500  feet 
head,  such  as  usually  occur  in  water-power  systems,  the  ordi- 
nary bell-and-spigot  joint  packed  with  lead  is  sufficient.  As 
regards  weight  of  pipes,  there  is  but  slight  economy  in  high 
pressure  and  small  volume  of  water  as  compared  with  low 
pressure  and  large  volume,  the  increased  diameter  of  the  pipe 


404  HYDRAULIC    TRANSMISSION. 

consequent  on  increased  volume  being  substantially  offset  by 
the  diminished  thickness  consequent  on  diminished  pressure. 

The  thickness  above  given  refers  to  cast-iron  pipes.  It  is 
very  probable  that  recent  improvements  in  metallurgy  would 
now  warrant  the  use  of  steel  pipes,  drawn,  forged,  or  welded, 
with  a  safe  tensile  strength  of  i  5  ooo  pounds  per  square  inch 
— an  improvement  calculated  to  greatly  extend  the  hydraulic 
transmission  of  power. 

A  pipe  of  novel  character  has  recently  been  used  to  conduct 
water  under  a  pressure  of  750  pounds  per  square  inch  for 
operating  the  movable  span  of  a  bridge  at  the  mouth  of  the 
river  Dee  in  England.  It  is  a  continuous  drawn  lead  pipe 
such  as  can  be  procured  in  great  lengths,  without  joints.  To 
give  it  the  necessary  strength  it  is  wound  externally  with 
copper  wire.  It  rests  on  the  bed  of  the  river  and  by  its  flexi- 
bility adjusts  itself  to  the  inequalities  of  the  bottom.  A  copper 
pipe  previously  used  put  together  with  ordinary  joints  had 
failed.  The  lead  pipe  has  worked  successfully.* 

Pumps. — The  installations  at  Zurich  and  at  Geneva  use  the 
Girard  pump,  which  consists  of  a  somewhat  long  cylinder 
divided  into  two  cylinders  by  a  central  diaphragm.  A  solid 
plunger  works  into  each  end  of  the  cylinder.  These  plungers 
carry  cross-heads  at  their  outer  ends  which  are  united  by  rods, 
forming  a  large  frame  to  which  a  reciprocating  movement  is 
communicated  by  a  crank,  one  plunger  moving  "outboard," 
while  the  other  moves  "inboard."  The  distinctive  advantage 
of  this  arrangement  is  that  it  has  no  packings  which  require  the 
dismemberment  of  the  machine  for  their  adjustment. 

In  the  Zurich  system  a  group  of  turbines  drives  a  horizontal 
shaft  by  means  of  bevel-gears.  This,  says  Mr.  Unwin,  runs  at  a 
speed  of  50  turns  per  minute  and  actuates  a  second  shaft  at  a 
speed  of  100  turns  per  minute.  To  the  latter  the  pumps  are 
coupled,  it  is  presumed  through  the  intervention  of  spur-gearing, 
as  a  crank  running  100  turns  would  give  them  too  high  a  velocity. 

*  Engineering  Xews,  vol.  XXXVII.  p.  17. 


APPLIED    TO  LOCKS.  405 

At  Geneva  each  turbine  drives  a  pair  of  Girard  pumps,  by 
means  of  a  crank  on  the  head  of  the  vertical  turbine-shaft. 
These  pumps  are  set  in  lines  at  right  angles  to  each  other,  and 
the  plungers  move  188  feet  per  minute,  the  stroke  being  3.61 
feet.  Another  form  and  arrangement  of  pump  will  be  described 
presently. 

It  has  always  appeared  to  the  writer  that  there  must  be 
some  more  rational  method  of  pumping  water  by  means  of 
water-power  than  by  using  the  water-power  to  drive  a  wheel 
and  the  wheel  to  drive  a  pump.  This  method  involves  two 
transformations  and  two  sources  of  waste,  when  there  should 
be  but  one.  He  would  suggest  to  inventors  to  turn  their 
attention  to  a  method  dispensing  wholly  with  the  water-wheel. 
Let  the  power-water  act  in  a  very  large  cylinder  to  give  motion 
to  a  piston  and  rod,  the  latter  carrying  at  its  opposite  end  a 
small  piston  acting  in  a  cylinder  and  forcing  the  water  into  the 
pressure-pipes. 

Hydraulic  Transmission  Applied  to  Locks.  —  Modern 
navigation  locks  have  attained  dimensions  which  call  for  con- 
siderable power  in  moving  the  gates.  Not  only  the  main  gates 
which  control  the  channel,  ordinarily  called  the  mitre  gates, 
but  the  sluice-gates  or  valves  for  the  admission  and  discharge 
of  water.  *  The  lock  recently  completed  at  St.  Mary's  Falls, 
Mich.,  has  a  length  of  800  feet,  a  width  of  100,  and  a  maxi- 
mum lift  of  2O  feet,  requiring  the  admission  and  discharge  of 
i  600  ooo  cubic  feet  of  water  at  every  lockage.  Such  dimen- 
sions call,  during  the  season  of  active  navigation,  for  the 
frequent  and  rapid  movement  of  massive  gates.  As  the  pur- 
pose of  a  large  lock  is  usually  to  pass  vessels  around  a  fall  or 
rapid  in  a  running  stream,  it  is  almost  invariably  associated 
with  water-power,  and  this  is  usually  the  most  economical 
source  of  energy  available  for  manipulating  the  gates.  More- 
over, the  power  being  required  at  a  number  of  points  some 
hundreds  of  feet  distant  from  the  source,  transmission  is  neces- 

*  Report  of  Chief  of  Engineers,  U.  S.  A.,  1898,  p.  2554. 


406 


HYDRA  ULIC   TRANSMISSION. 


sary,  and  water  under  pressure  is  usually  the  most  economical 
means.  The  writer  gives  the  following  description  of  a  system 
designed  by  himself  and  applied  to  a  lock  on  the  Muscle  Shoals 
Canal,  on  the  Tennessee  River,  in  Alabama.  This  lock  was 
not  of  the  largest  class,  being  about  300  feet  long  from  hollow 
groin  to  hollow  groin  and  60  feet  wide,  with  a  lift  of  8  or  10 
feet.  There  are  two  pairs  of  mitre-gates  swinging  horizontally 
and  several  sluice-gates  moving  up  and  down  for  filling  and 
emptying  the  lock-chamber,  150000  to  180000  cubic  feet  of 
water  being  required  for  each  lockage. 

A  parallel-flow  wheel  some  40  inches  external  diameter 
was  inserted  in  a  pit  formed  in  one  of  the  approaches  of  the 
lock.  The  head  of  the  vertical  shaft  was  disposed  as  indicated 
in  Fig.  198.  It  had  a  square  neck  which  entered  a  sort  of  hub 


FIG.  198. 

B  revolving  in  a  fixed  bearing.  This  arrangement  allowed 
the  wheel  to  sink  by  the  wearing  of  the  step  without  bringing 
any  strain  on  its  upper  supports.  This  hub  forms  a  part  of  the 
crank,  which  revolves  with  the  wheel,  and  carries  the  crank- 
pin  C.  This  crank-pin  carries  a  circular  disk  to  which  are 
attached  the  pump-rods  ee  of  six  pumps  arranged  in  a  circle, 
with  the  wheel-shaft  in  the  centre.  These  pumps  are  worked 
by  hollow  plungers  f,  to  the  bottom  of  which  the  pump-rod  e 
is  jointed,  an  arrangement  which  gives  sufficient  play  to  the 
pump-rod  within  the  hollow  plunger  and  dispenses  with  a  con- 
necting-rod. The  crank-pin  C  is  adjustable  by  means  of  a 
screw  d  giving  the  pump-plungers  a  greater  or  less  stroke 


APPLIED    TO   LOCKS. 


407 


according  to  the  fall  available.  The  wheel  is  only  intended 
to  run  while  the  lock  is  in  use,  and  the  pipes  are  provided  with 
a  relief-valve,  adjusted  to  the  .desired  pressure,  for  wasting  the 
superfluous  water.  One  of  the  rods  c  is  rigidly  fastened  to  the 
disk,  the  rest  are  jointed.  The  discerning  reader  will  see  that 
the  device  would  not  operate  if -all  the  rods  were  jointed,  neither 


FIG.  199. 

would  it  do  so  if  more  than  one  were  rigidly  attached.  Small 
pipes  conduct  the  water  from  the  pumps  to  the  several  points 
of  use.  The  sluice-gates  are  raised  and  lowered  by  hydraulic 
cylinders  with  piston-rods  attached  to  the  gates.  The  mitre- 
gates  are  swung  by  a  hydraulic  engine  of  a  peculiar  form, 
Figs.  199  and  200,  called  a  crab.  This  is  a  quadrantal  case 


4O5  HYDRAULIC   TRANSMISSION. 

with  a  rectangular  piston  having  an  angular  traverse  of  60  or 
70  degrees,  equal  to  the  swing  of  the  gate  in  opening  or  clos- 
ing. The  piston  consists  of  a  hollow  cylinder  with  a  wing 
attached.  Passing  through  the  cylindrical  part  is  a  short  shatt 
placed  directly  over  the  heel-post  and  united  thereto  by  an 
Oldham  coupling,  i.e.,  a  coupling  which  admits  of  a  slight 
deviation  from  a  straight  line  in  the  centres  of  the  shafts  united. 
A  good  deal  of  leakage  is  to  be  expected  in  this  arrangement, 
but  this  is  not  material,  as  there  is  abundant  power  and  ques- 

SECTION 


FIG.  200. 

tions  of  economy  do  not  enter.  The  swinging  of  the  gate  is 
accomplished  by  a  four-way  valve  which  alternately  admits  the 
water  to  one  side  of  the  piston  while  discharging  it  from  the 
other.* 

Efficiency  of  Hydraulic  Transmission. — We  may  generally 
count  upon  an  efficiency  of  80  per  cent  in  the  hydraulic  motor, 
i.e. ,  the  power  communicated  to  the  pump  is  80  per  cent  of  the 


*  For    more    detailed    illustrations    of   this  mechanism,  see  Report  of 
Chief  of  Engineers,  U.S.A.,  1890,  p.  2111. 


STORAGE   OF  ENERGY  BY  PUMPING.  409 

water-power  expended.  This  is  only  true  when  the  head  is 
measured  close  to  the  wheel.  When,  as  is  more  commonly 
the  case,  the  head  appertinent  to  the  water-power  represents 
the  descent  from  the  pond  or  canal  to  smooth  water  below  the 
wheel,  not  more  than  75  per  cent  can  be  expected.  A  loss  of 
as  much  as  12  per  cent  must  be  expected  in  pumping,  and 
ordinarily  as  much  as  5  per  cent  in  transmission  through  the 
pipes.  An  efficiency  of  80  per  cent  may  be  assumed  in  the 
motors  through  which  the  water  acts  to  drive  machines.  Thus, 
the  percentage  of  the  gross  power  which  can  be  imparted  to 
machinery  at  a  distance  of  a  mile  or  more  from  the  source  is 
not  more  than  0.75  X  O.88  X  0.95  X  0.80  =  0.50. 

Storage  of  Energy  by  Pumping. — In  the  ordinary  case  of 
a  water-power  on  a  running  stream,  there  is  a  great  super- 
abundance of  water  at  certain  seasons  of  the  year,  and  a 
deficiency  at  others.  It  is  a  very  natural  suggestion  that  the 
surplus  energy  of  wet  months  could  be  employed  in  pumping 
water  into  a  high  reservoir  for  use  during  the  dry  months.  At 
most  water-powers  there  is  a  surplus  of  power  six  months  in 
a  year,  and  the  case  is  very  rare  when  water  does  not  run  to 
waste  fully  four  months  in  the  year.  A  pumping-plant  could 
run  during  these  periods  night  and  day,  and  could  accumulate 
a  large  store  for  use  during  the  ensuing  time  of  scarcity.  The 
chief  difficulty  in  such  a  project  is  to  find  a  suitable  site  for  the 
reservoir,  and  when  a  sufficient  elevation  exists  it  is  usually 
on  the  summit  of  a  hill  where  the  construction  would  be 
inordinately  expensive.  Another  difficulty  is  that  in  using  the 
variable  flow  of  the  stream  it  would  be  necessary  to  install  two 
or  three  horse-power  of  plant  in  order  to  obtain  an  average 
effect  of  one  horse-power.  The  interest  and  depreciation  on 
this  plant  will  usually  be  found  to  more  than  offset  the  advan- 
tage to  be  expected  from  it. 

Nevertheless,  in  textile  mills  running  10  hours  or  less  per 
day,  where  a  suitable  reservoir-site  exists,  the  following  project 
will  often  be  found  well  worthy  of  consideration :  To  adapt  the 
wheels  to  the  driving  of  pumps,  so  that  on  the  cessation  of  each 


410  HYDRAULIC    TRANSMISSION. 

day's  work  they  can  readily  be  changed  to  that  duty,  and  to 
keep  them  employed  in  non-working  hours,  during  the  season 
of  abundant  water,  in  raising  water  to  the  reservoir  for  use  in 
the  dry  period.  A  wheel  of  200  h.p.  working  twelve  hours 
would  raise  water  sufficient  for  6  X  200  =  1200  h.p.  hours, 
and  during  six  months  of  abundant  water  would  accumulate 
enough  to  maintain  200  h.p.  for  nearly  four  months  of  deficient 
flow,  and  under  ordinary  conditions  a  wheel  could  raise  enough 
during  the  period  of  abundance  to  carry  the  work  through  the 
period  of  scarcity.  It  is  true  that  the  power  obtained  is  only 
half  that  expended,  but  the  power  obtained  is  useful  power,  and 
that  expended  is  of  no  value. 

A  desideratum  in  this  mode  of  running  would  be  a  hydraulic 
engine  capable  of  acting  as  a  pump  propelled  by  a  shaft,  to 
raise  water  to  the  reservoir  during  the  season  of  abundance, 
and  as  a  motor  to  drive  or  aid  in  driving  the  same  shaft  during 
the  season  of  scarcity.  It  is  true  that,  in  order  to  do  a  given 
amount  of  work  on  the  shaft,  a  larger  quantity  of  water  must 
pass  the  engine  when  running  as  a  motor  than  when  running 
as  a  pump.  This  condition  can  be  met  by  the  adjustable 
crank-pin. 


CHAPTER   XX. 

PNEUMATIC  TRANSMISSION   OR   TRANSMISSION   BY 
COMPRESSED    AIR. 

AIR,  like  water,  may  be  transmitted  under  a  high  pressure, 
and  render  up,  at  the  receiving  end  of  the  line,  a  considerable 
fraction  of  the  power  expended  in  compressing  it.  The  differ- 
ence in  the  methods  of  transmission  by  air  and  by  water  results 
wholly  from  the  difference  in  weight  and  compressibility  of 
these  two  media.  Water  is  practically  incompressible,  and  the 
piston  employed  in  forcing  it  works  under  a  uniform  pressure 
during  the  entire  stroke.  At  an  elevation  corresponding  to 
the  pressure  it  may  be  confined  in  an  open  reservoir.  Air, 
for  practical  purposes,  may  be  regarded  as  compressible  with- 
out limit.  The  piston  employed  in  compressing  it  undergoes, 
during  a  single  stroke,  all  gradations  of  pressure  from  that  of 
the  atmosphere  to  that  of  the  pressure-pipe.  It  requires  closed 
vessels  for  its  retention.  Its  volume  must  be  greatly  reduced 
in  putting  it  under  the  required  pressure,  and  the  pressure 
exerted  during  the  resumption  of  its  original  volume,  called 
the  expansive  pressure,  must  be  utilized  in  the  development 
of  the  power,  if  the  latter  is  to  approach  in  any  reasonable 
degree  the  power  expended  in  compressing  the  air. 

Compressed  air  is  much  employed  in  mining,  quarrying, 
ami  tunnel-work.  In  the  construction  of  great  locks,  dams, 
reservoirs,  bridges,  and  other  important  works  where  a  great 
many  isolated  machines,  such  as  power-drills,  stone  crushing 
and  dressing  machines,  grindstones,  mortar-  and  concrete- 
mixers, repair-works,  and  hoists,  have  to  be  operated  at 
different  points,  it  is  coming  into  general  use  as  a  means  of 

411 


412  PNEUMATIC    TRANSMISSION. 

distributing  small  quantities  of  power  from  a  central  station. 
As  examples  we  may  mention  the  reservoir  for  the  New  York 
water-works  now  under  construction  at  Jerome  Park,  and  the 
lock  at  Meeker's  Island  on  the  Mississippi  between  St.  Paul  and 
Minneapolis.  A  system  of  pumping  sewage  at  a  number  of 
isolated  stations  by  compressed  air  supplied  from  a  central 
station  has  recently  been  perfected  by  Mr.  Isaac  Shone  and 
is  finding  some  application.  In  London  compressed  air 
carried  in  a  strong  vessel  has  been  extensively  used  for  the 
propulsion  of  street-cars. 

"Compressed-air  transmission,"  says  Mr.  Unwin,  "is  a 
perfectly  general  method  of  distributing  power  for  all  purposes. 
Whether  in  any  given  case  it  is  the  most  advantageous,  the 
least  wasteful  of  power,  or  the  cheapest  in  working  cost 
depends  on  various  circumstances.  M.  Hanarte  believes  that 
it  is  and  will  contiune  to  be  the  most  economical  method  of 
transmission  to  considerable  distances.  The  loss  in  the  air- 
mains  is  very  small.  The  motors  worked  expansively  are 
efficient.  The  mains  can  be  carried  by  any  path,  and  the 
differences  of  elevation  between  the  compressing  and  working 
points  do  not  sensibly  affect  the  results.  In  hydraulic  transmis- 
sion the  water  must  be  collected,  stored,  and  in  some  cases 
filtered,  and  having  actuated  a  motor,  means  must  be  found  for 
removing  it.  But  air  is  everywhere  available  and  can  be 
•discharged  anywhere  without  causing  trouble.  Compressed  air 
has  peculiar  advantages  in  the  case  of  underground  transmis- 
sions. It  has  been  used  to  replace  manual  labor  in  situations 
where  hardly  any  other  motive  power  could  have  been  em- 
ployed." 

Compressed  air  is  susceptible  of  indefinite  subdivision  and 
•of  measurement  of  the  quantity  supplied  to  each  consumer. 
The  latter  is  not  so  simple  as  in  the  case  of  pressure-water,  but 
presents  no  mechanical  difficulty.  Meters  similar  to  gas-meters 
.are  used  which  are  not  costly  and  which  register  the  quantity 
-of  air  with  sufficient  accuracy  for  commercial  purposes.  The 
pipes  are  less  costly  than  for  water-pressure  and  liable  to  less 


RELATIONS   OF   VOLUME  AND    PRESSURE  IN  AIR.     413 

loss  from  leakage.  We  have  seen  that  a  1 2-inch  pipe  would 
transmit  463  h.p.  with  water  at  750  pounds  per  square  inch. 
An  air-pipe  of  equal  size  at  7  atmospheres  would  deliver  con- 
siderably more,  and  need  not  be  a  third  part  as  heavy  as  the 
water-pipe.  Moreover,  the  air-pipes  do  not  need  the  same 
precautions  for  protection  against  frost. 

The  disastrous  consequences  that  sometimes  result  from  the 
sudden  stoppage  of  the  current  in  a  water-pipe  or  from  the 
breach  of  the  pipe  have  no  parallel  in  the  air  system.  The 
bursting  of  a  receiver  is  a  case  parallel  to  the  breach  of  an 
elevated  reservoir,  but  the  consequences  only  reach  a  very 
limited  area. 

Compressed  air  is  susceptible  of  useful  applications  other 
than  the  development  of  power — applications  which  do  not 
pertain  to  any  other  known  form  of  energy.  In  foundations 
and  tunnels  water  is  excluded  by  an  atmosphere  of  compressed 
air.  It  can  generate  light  by  driving  a  dynamo.  The  exhaust 
of  the  air-engine  can  be  used  for  refrigerating  purposes,  for 
cooling  and  ventilating  rooms,  for  forced  draft  of  furnaces. 

Relations  of  Volume  and  Pressure  in  Air. — In  considering 
questions  of  this  kind  it  is  convenient  to  fix  attention  upon  a 
definite  quantity  of  air,  say  one  pound. 

Suppose  Pl  to  represent  the  pressure  and  vl  the  volume  of 
compression ;  P2  the  pressure  and  vz  the  volume  of  release, 
which  is  usually  at  atmospheric  pressure ;  P  any  pressure,  and 
v  the  corresponding  volume.  It  is  sometimes  convenient  to 
consider  Pl,  P2 ,  P  as  the  pressures  upon  a  square  foot  instead 
of  a  square  inch  as  is  usual.  The  standard  atmospheric  pres- 
sure per  square  foot  is  2116.4  pounds. 

For  Isothermal  Change  of  Volume,  i.e.,  when  air  during 
change  of  volume  is  maintained  at  a  constant  temperature, 
Plvl  =  P2v2  —  Pv.  For  a  temperature  of  60°  F.  Pv  =  27  709 
foot-pounds. 

For  convenience,  imagine  the  change  of  volume  to  take 
place  in  a  cylinder  of  one  square  foot  cross-section,  then  v2 


414  PNEUMATIC   TRANSMISSION. 

represents  the  total  stroke,  vl  the  portion  of  stroke  performed 
under  full  pressure. 

The  work  done  during  an  indefinitely  small  portion  of  the 

dv 

stroke   dv  is  dw  —  Pdv  =  P.v, — .      The  total  work  between 

1  v 

the  limits  v  =  c\  and  v  =  v2  is 

P^\  hyperbolic  log.  —*•....      (63) 

This  represents  the  work  required  to  compress  a  pound  of  air 
from  the  volume  ?'2  to  the  volume  z'r  It  also  represents  the 
work  yielded  by  a  pound  of  air  in  an  engine,  entering  at  the 
pressure  Pl  and  expanding  to  the  pressure  P.r  The  expression 
does  not  specifically  include  the  work  of  admission  nor  exclude 
the  work  done  against  the  pressure  of  the  atmosphere.  The 
former  is  Plvl ,  and  the  latter  P2v2 ,  and  as  these  are  equal  they 
mutually  offset  each  other. 

For  Adiabatic  Change  of  Volume,  i.e.,  when  the  air  neither 
receives  nor  parts  with  heat  during  the  process,  we  have 


so  that  />  =  />^_JL 

and  the  work  due  to  an  elementary  change  of  volume  is 
dw  =  Pdv  =  Pi\~}'4   dv  =  Py^V^dv. 

The  integral  of  this  expression  between  the  limits  v  =  v^  and 

v  =  v.2  is 

i 


0.408  v 


or  putting  R  to  represent  the  ratio  of  expansion  =  —  , 

vi 

t  ,  l  \  o.4o8» 

lvli-  .     .     .     .     (64) 


ADIABATIC  CHANGE   OF  VOLUME.  41$ 

This  expression  represents  only  the  work  of  compression  or 
expansion,  not  the  total  work.  In  developing  power,  the  work 
done  by  the  air  includes  admission  P{c\ ,  and  excludes  the  work 
P2v2  consumed  in  atmospheric  resistance.  These  are  not,  in 
this  case,  equal  to  each  other.  In  compression,  the  work 
expended  includes  the  work  of  forcing  the  air  into  the  receiver 
or  pipes  after  it  has  reached  the  pressure  Pl ,  and  excludes  the 
work  done  by  atmospheric  pressure  acting  on  one  side  of  the 
compressing  piston.  The  expression  representing  the  net  work 
done  in  compressing  a  pound  of  air  to  the  pressure  Pl ,  or  the 
net  work  yielded  by  the  same  after  compression,  is 

-P2vr      .      (65) 

The  process  of  compression  is  attended  by  a  great  develop- 
ment of  heat,  which  increases  the  tension  of  the  air  and 
consequently  the  work  of  compression.  Were  the  stroke  of 
compression  followed  immediately  by  the  stroke  of  expansion, 
the  power  developed  would  be  exactly  equal  to  the  power 
expended.  This,  however,  never  occurs.  The  air  after  com- 
pression, is  transmitted  through  pipes  to  a  distant  point,  and 
unavoidably  cools  to  the  temperature  of  the  external  air  or 
earth,  so  that  the  power  obtainable  from  it,  without  an  addition 
of.  heat,  falls  greatly  below  that  expended  in  compressing  it. 
This  is  the  inherent  defect  of  the  system  of  transmission  by 
compressed  air.  As  to  the  loss  in  compression,  this  can  be 
diminished,  but  not  wholly  avoided,  by  the  use  of  means  to 
absorb  the  heat.  As  to  expansion,  a  very  inconsiderable  addi- 
tion of  heat  will  not  only  obviate  the  loss  but  transform  it  into 
a  gain. 

The  full  theory  of  this  subject  involves  the  science  of  heat, 
which  cannot  be  gone  into  in  this  treatise.  Those  who  wish 
to  pursue  it  should  study  Rankine  on  the  Steam-engine, 
Weisbach  ("Heat  and  Steam"),  Zeuner,  Maxwell,  Tait,  and 
other  writers  who  have  exhaustively  treated  the  subject. 

The  accompanying  tables  give  a  practical  idea  of  the  rela- 


PNEUMATIC   TRANSMISSION. 


tions  of  volume,  pressure,  and  temperature  in  compressed  air. 
Table  9  gives  the  power  required  to  compress  a  pound  of  air 
from  atmospheric  pressure  to  different  pressures  up  to  100 
pounds  per  square  inch.  The  pressure  Pl  is  the  absolute 
pressure  of  the  air,  which  is  supposed  to  be  maintained  con- 
stantly at  a  temperature  of  60  degrees.  Omitting  unavoidable 
losses  from  friction  and  resistance  to  movement,  the  power 

TABLE   9.— ISOTHERMAL   CHANGE   OF   VOLUME;   Pv. 
CONSTANT  =  27709. 


I 

2 

3 

4 

s 

Pressure  of  Com- 
pression, Pounds 
per  Square  Inch. 

PI 

Volume  of 

Compressed  Air, 
Cubic  Feet. 

Ratio  of  Volumes 
and  Pressures, 

PL^VS 

Power  required 
to  Compress 
i  Pound  of  Air 
from  PZ  to  />,. 
Foot-pounds. 

Power  required 
to  Compress 
i  Pound  of  Air 
per  Second. 
Horse-power. 

IOO 

1.925 

6.  So 

53  "8 

96.5 

95 

2.O26 

6.46 

5i  705 

94 

90 

2.139 

6.12 

50  208 

91 

85 

2.265 

5.78 

48  629 

88 

80 

2.406 

5-44 

46946 

85 

75 

2.567 

5.10 

45  154 

82 

70 

2.750 

4.76 

43  245                       79 

65 

2.962 

4.42 

41  189                     75 

60 

3.208 

4.08 

38972                     71 

55 

3-500 

3-74 

36562                     66.5 

50 

3-850 

3-40 

33921 

62 

45 

4.279 

3-06 

31  ooi 

56 

40 

4.809 

2.72 

27737 

50 

35 

5.500 

2.38 

24038 

44      • 

30 

6.417 

2.04 

19  766 

36 

expended  in  compressing  the  air  is  the  same  as  that  obtainable 
from  it  in  an  engine  which  expands  it  to  atmospheric  pressure. 
That  is  to  say:  If  air  could  be  maintained  at  uniform  tem- 
perature during  compression  and  expansion,  there  would  be  no 
loss  inherent  in  this  method  and  peculiar  to  it.  The  fifth 
column  gives  with  the  same  omission  the  number  of  horse- 
power expended  in  compressing  a  pound  of  air  per  second  o»- 
furnished  by  the  same  when  used  in  an  engine  admitting  of  its 
expansion  to  atmospheric  pressure.  In  practice  the  power 
expended  would  be  somewhat  in  excess  of  these  figures,  and 


AD  IAEA  TIC   CHANGE   OF   VOLUME. 


417 


that   obtained   would  fall   short   of  them.      In   addition   there 
'would  be  a  certain  loss  in  the  transmission-pipes. 

Tables  10  and  II  exhibit  the  conditions  incident  to  the 
compression  and  expansion  of  air  without  gain  or  loss  of  heat. 
To  compress  a  pound  of  air  from  atmospheric  pressure  and  60 
degrees  temperature  to  100  pounds  requires  70  987  foot-pounds 

TABLE  10.— POWER  REQUIRED  TO  COMPRESS  1  POUND  OF  AIR 
FROM  ATMOSPHERIC  PRESSURE  AND  60  DEGREES  TEM- 
PERATURE WITHOUT  GAIN  OR  LOSS  OF  HEAT. 


I                               2                                  3 

4                     5 

6 

8 

After  Compression. 

Power 

Ratio  of 
Pressure. 

P* 

Cut-off. 

Total 
Power 
Ex- 
pended. 

Expended 
excluding 
Atmospheric 
Pressure. 

Power  to 
Compress  i 
Pound  of  Air 
per  Second. 

Pressure 
in  Pounds 

Volume  in 

Cii     Wt 

Tempera- 

per  Sq.  In. 

u.  r  t. 

Degrees, 

Pl 

~R 

Foot-lbs. 

Foot-lbs. 

Horse- 
power. 

100 

3-3510 

448 

0.147    j      0.256 

98696 

70987 

129 

95 

3-4767 

434 

O.I55    i      0.266 

96358 

68649 

125 

90 

3-6I4I 

421 

0.163 

0.277 

93950 

66  241 

120 

85 

3-7637 

406 

0.173 

0.287 

90957 

63248 

"5 

80 

3-9283 

390 

0.184 

0.3OO 

88277 

60568 

no 

75 

4.1129 

373 

0.196         0.314 

85360 

57651 

105 

70 

4-3210 

358 

O.2IO 

0.330 

82375 

54666 

99 

65 

4-5553 

34i 

0.226          0.347 

79052 

51343 

93 

60 

4.8197 

322 

O.245           0.368 

75740 

48031 

87 

55 

5.1286 

303 

0.267           0.392 

71234 

43  525 

79 

50 

5.4860 

282 

0.294          0.419 

68414 

40705 

74 

45 

5.9140 

259 

0-327    i       0.452 

64347 

36638 

67 

40 

6.4285 

235 

0.367           0-49I 

59  881 

32172 

58 

35 

7.0686 

209 

O.420 

0.540 

55035 

27326 

50 

30        7.8867 

1  80 

0.490 

0.602 

49650 

21  941 

40 

of  energy.  The  air  so  compressed  has  a  volume  of  3.35  cubic 
feet  and  a  temperature  of  448  degrees  F.  In  the  course  of 
transmission  to  a  distance  of  several  miles  the  air  unavoidably 
cools  to  the  surrounding  temperature,  say  60  degrees.  If  we 
suppose  the  volume  of  the  air  to  remain  unchanged,  it  would  at 
the  latter  temperature  have  a  pressure  of  only  57-34  pounds. 
In  this  state,  led  into  an  engine  and  expanded  without  addition 
of  heat  to  atmospheric  pressure,  it  has  a  temperature  of  —  1 10°, 
and  a  volume  of  8.82  cubic  feet,  and  yields  only  31121  foot- 


41 8  PNEUMATIC   TRANSMISSION. 

pounds  of  energy,  viz.,  44  per  cent  of  the  power  expended". 
Even  from  this  low  percentage  must  be  deducted  the  losses  due 
to  friction  and  resistance  to  motion. 

TABLE  11.— POWER  OBTAINABLE  FROM  1  POUND  OF  COM- 
PRESSED AIR  EXPANDED  WITHOUT  GAIN  OR  LOSS  OF 
HEAT  TO  ATMOSPHERIC  PRESSURE,  AFTER  BEING  COOLED, 
TO  60  DEGREES. 


I                            2 

3                  4 

5 

6 

7 

8 

9 

10 

Pressure  in  Pounds 

AT          nh 

per  Square  Inch. 

Pressure. 

Power 

Power 

Gross 

due  to 

Fur- 

Ratio of 

Cut-off 

Power 

Atmos- 

Net 

nished 

After 

Pressure 

Obtain- 

pheric 

Power. 

bv  i  Ib. 

Of  Com- 

Cooling 

Temper- 

Volume. 

able. 

Resist- 

of Air 

pression. 

to  60 

ature, 

Cubic 

PI 

i 

ance. 

per  Sec.. 

Degrees. 

Degrees, 

Feet. 

p 

^ 

Pl 

>. 

P. 

r, 

Foot-lbs. 

Foot-lbs. 

Ft.-lbs. 

H.-P. 

100 

57-34 

—  iro 

8.82 

0.256 

0.380 

49  791 

18  670    31  121 

56.6 

95 

55-30 

-106 

8.92 

0.266 

0.390 

49333 

18  882     30451 

55-4 

90 

53-17 

—  102 

9.02 

0.276 

0.401 

43779 

19094  ;  29685 

54-0 

85 

51.11 

-    98 

9.12 

0.288 

0.413 

48265 

19305  |  28  960;      52.7 

80 

48.96 

—  93 

9.24 

0.300 

0.425]  47700 

19559  ;  28141     51.2 

75 

46-59 

-   88 

9-37 

0.315 

0-439 

46889 

19834   27055     49.2 

70 

44-53 

-  83 

9-50 

0.330 

0-455 

46369 

20  IIO    :26259|       47.7 

65 

42.24 

77 

9-65 

0.348 

0.472 

45624 

20427 

25197       45-8 

60 

39-92 

-  71 

9.80 

0.368 

0.492 

44770 

20745 

24025 

43-7 

55 

37-52 

-  64 

9-97 

0.392 

0.514 

43858 

21   104      22754 

41.4 

50 

35.06 

-   56 

10.17 

0.419 

0-539 

42  828 

21  528 

21  3ooj     38.7 

45 

32-58 

-  47 

10.40 

0.451 

0-569 

41721 

22015 

19  706 

35-8 

40 

29-94 

-  37 

10.65 

0.491 

0.604 

40343 

22  544 

17799 

32-4- 

35 

27.21 

-   25 

10.95 

0.540 

0.646 

38781 

23179 

15  602 

28.4 

30 

24-39 

—   ii   1   11.30 

0.602 

0.698 

36959 

23920 

13039 

23-7 

It  is  obvious  from  the  foregoing  that  the  success  of  any 
system  of  air-transmission  depends  very  largely  upon  the 
efficiency  of  the  means  employed  for  absorbing  the  heat  of 
compression  and  supplying  the  heat  of  expansion.  If  the 
former  be  thoroughly  done,  and  the  air  before  admission  to  the 
engine  be  sufficiently  heated,  the  power  obtained  may  not  only 
equal  but  even  exceed  that  expended  in  compression.  With- 
out such  heating  the  use  of  air  at  high  pressures  is  impracti- 
cable, owing  to  the  formation  of  ice  on  the  valves  of  the  engine 
due  to  the  extremely  low  temperature  of  release.  Power 
developed  by  compressed  air  is  substantially  the  mechanical 


THE  AIR-COMPRESSOR.  419 

•equivalent  of  the  heat  which  disappears  in  expansion.  Coal 
used  in  heating  the  air,  if  we  credit  the  coal  with  the  entire 
power  developed  by  the  air,  furnishes  power  at  the  rate  of  3  or 
4  horse-power  per  pound  of  coal  per  hour ;  whereas  the  most 
efficient  steam-engines  do  not  in  practical  working  furnish  more 
than  i  brake  horse-power  for  every  2|  pounds  of  coal  per  hour. 
A  pound  of  coal  per  hour  to  every  3  or  4  horse-power  is  so 
trifling  an  expense  as  to  be  hardly  worth  considering.  Theo- 
retically it  should  take  a  little  more  than  I  pound  of  coal 
to  6  horse-power. 

The  Air-compressor.  —  Air  is  compressed  by  a  piston 
moving  in  a  cylinder.  The  pressure  opposing  the  piston  is 
very  slight,  in  fact  nothing,  at  the  commencement  of  the  stoke, 
and  becomes  great  toward  the  end  — a  condition  which  intro- 
duces a  serious  difficulty  into  the  design  and  operation  of  the 
machine.  In  the  case  we  are  considering,  viz.,  where  the 
motive  power  is  furnished  by  a  water-wheel,  the  latter  v/orks 
most  efficiently  with  a  uniform  resistance  at  all  p  hits  of  its 
revolution.  When  applied  to  an  air-compressor  making  a 
forward  and  return  stroke  at  each  revolution,  the  power  of  the 
wheel  is  greatly  in  excess  of  the  resistance  at  the  commence- 
ment of  the  stroke,  and  only  becomes  equal  to  it  when  the  air 
has  reached  the  required  pressure  and  is  being  forced  into  the 
receiver.  The  wheel  takes  an  irregular  velocity,  starting 
forward  at  the  commencement  of  the  stroke  and  slowing  up  at 
the  end.  The  power  of  the  wheel  in  excess  of  the  resistance 
of  the  air  is  lost,  and  its  working  is  very  wasteful.  When  the 
wheel  runs  on  a.  horizontal  shaft  this  difficulty  is  remedied  by 
a  fly-wheel,  but  the  latter  is  not  applicable  on  a  vertical  shaft. 
It  is  sometimes  avoided  in  a  measure  by  arranging  a  number 
of  single-acting  compressors  in  a  circle,  all  driven  from  a  crank 
on  the  vertical  shaft,  as  in  the  case  of  the  force-pumps  described 
page  405.  When  the  power  is  derived  from  a  steam-engine, 
the  compressing  piston  being  on  the  same  rod  as  the  steam- 
piston,  the  condition  is  still  more  uneconomical.  In  fact  it  is 
precisely  the  reverse  of  economical.  The  pressure  on  the 


420  PNEUMATIC   TRANSMISSION. 

steam-piston  is  great  at  the  commencement  of  the  stroke  and 
diminishes  to  nearly  nothing  at  the  end,  whereas  the  pressure 
on  the  air-piston  is  extremely  slight  at  the  commencement  and 
becomes  great  toward  the  end.  This  difficulty  is  very  effec- 
tually met  by  a  heavy  fly-wheel. 

To  absorb  the  heat  generated  by  compression  and  prevent 
the  air  from  exerting  a.  greater  pressure  during  compression 
than  during  expansion,  the  most  effective  means  is,  first,  to 
surround  the  compressing  cylinder  with  cold  water  in  constant 
circulation,  and,  second,  to  inject  cold  water  into  the  cylinder 
in  the  form  of  a  fine  spray.  This  latter  expedient  is  very 
effective,  but  is  attended  with  constructive  difficulties.  It  is 
important  that  the  clearance-space  between  the  piston  and  the 
cylinder-head  should  be  as  small  as  possible,  because  the  air 
contained  therein  represents  so  much  waste  of  power — air 
compressed,  but  not  secured  in  the  receiver.  When,  however, 
this  space  is  too  much  reduced  there  is  danger  that  the  injection- 
water  will  more  than  fill  the  clearance  and  cause  a  rupture  of 
the  cylinder-head,  as  often  occurs  in  steam-engines  from  the 
accumulation  of  condensed  water. 

Engines  Worked  by  Compressed  Air  are  in  no  essential 
respect  different  from  non-condensing  steam-engines,  and 
require  no  additional  appurtenances  or  attachments  except  a 
cock  for  injecting  a  spray  of  water  into  the  cylinder.  Even 
when  the  air  is  heated  before  admission  this  spray  of  water  is 
found  very  advantageous.  The  process  of  heating  consists  in 
transferring  to  the  air  the  heat  of  the  gases  arising  from  the 
combustion  of  the  fuel.  This  process  is  very  simple  in  the  case 
of  air  compared  with  the  generation  of  steam,  where  the  gases, 
after  leaving  the  boilers  must  retain  heat  enough  to  create  a 
draft  up  the  chimney.  The  exhaust  air  from  the  engine  slightly 
raises  the  pressure  in  the  engine-room  and  creates  a  current 
through  any  aperture  or  passage  leading  to  the  open  air. 
There  is  no  necessity  for  a  chimney  to  create  a  draft.  The  air 
may  approach  the  engine-room  through  a  pipe  of  such  size  as 
to  give  it  a  low  velocity.  Enclosed  in  this  pipe  is  another 


RAISING   LIQUIDS.  421 

which  conducts  the  furnace-gases  under  the  pressure  of  the 
exhaust.  The  current  of  air  to  be  heated  moves  in  the  oppo- 
site direction  to  the  heating  current.  At  all  points  of  this  pipe 
the  gases  are  warmer  than  the  air  and  in  a  condition  to  impart 
heat  to  the  same.  The  air-pipe  has  a  non-conducting  coating, 
and  all  the  heat  generated  by  the  fuel  can  thus  be  transferred 
to  the  air. 

The  air  can  also  be  heated  by  petroleum  burned  within  the 
air-pipe  or  by  illuminating-gas  burned  within  the  inner  flue. 
There  has  recently  been  a  marked  cheapening  of  illuminating- 
gas  and  it  is  now  extensively  used  for  heating.  The  ideal 
system  of  transmission  and  distribution  of  power  by  compressed 
air  in  point  of  efficiency,  cleanliness,  and  convenience  would 
be  a  system  of  air-pipes  combined  with  a  system  of  pipes  for 
the  distribution  of  gas. 

In  southern  latitudes  the  system  of  air-transmission  recom- 
mends itself  strongly  on  account  of  its  applicability  to  purposes 
of  cooling  and  ventilation.  By  controlling  the  heat  imparted 
to  the  air  the  exhaust  can  be  delivered  at  any  desired  tempera- 
ture and  serve  either  for  warming  or  cooling  the  work-rooms. 
Where  required  for  refrigeration  only,  a  small  motor  can  be 
run  to  drive  a  compressor,  forcing  air  into  the  pipes,  thus 
partly  compensating  for  the  air  drawn,  and  delivering  the 
exhaust  at  a  very  low  temperature. 

Raising  Liquids. — Beer  and  other  liquids  are  raised  from 
cellars  to  the  upper  parts  of  buildings  by  connecting  the  tanks 
or  barrels  containing  the  liquid  with  the  air-pipes.  Com- 
pressed air  is  employed  to  raise  water  from  non-flowing  artesian 
wells,  without  pumps  or  mechanism  of  any  kind.  The  depth 
of  water  in  the  well  should  be  four  or  five  times  the  lift.  A 
small  pipe  is  carried  down  to  near  the  bottom  of  the  well  and 
delivers  air  into  the  water.  The  air,  diffusing  itself  through 
the  water  of  the  well,  lightens  the  aggregate  mass  so  that  it 
exerts  less  pressure  at  the  bottom  than  the  source  from  which 
it  is  supplied.  The  water  consequently  rises  and  overflows. 
The  pressure  of  the  air  in  this  application  should  be  but  little 


422  PNEUMATIC  TRANSMISSION. 

greater  than  that  due  the  depth  of  water  at  the  point  of  delivery. 
The  air  expands  isothermally  in  rising,  the  heat  for  maintaining 
the  temperature  being  derived  from  the  water. 

Compressed-air  Installation  of  Paris.  —  About  1870  a 
system  of  small  pipes  was  laid  down  in  Paris  for  the  purpose 
of  actuating  clocks  throughout  the  city  by  means  of  compressed 
air.  Some  eight  thousand  clocks,  public  and  private,  came  into 
the  system,  all  moved  isochronously  by  impulses  transmitted 
through  the  air-pipes.  This  installation  gradually  grew  into 
the  furnishing  of  air  from  a  central  station  for  purposes  of 
motive  power.  New  and  larger  compressing  stations  were 
erected  and  larger  pipes  laid,  till  in  1889  the  system  required  a 
compressing  plant  of  some  8000  horse-power.  About  1891  a 
new  station  was  erected  at  the  Quai  de  la  Gare  contemplating 
the  ultimate  use  of  some  24  ooo  horse-power.  There  were  at 
that  time  something  over  10  miles  of  pipe  for  the  transmission 
of  air.  In  the  early  history  of  the  enterprise  the  pressure  was 
about  45  pounds  per  square  inch  absolute ;  later  a  pressure  of 
90  has  been  adopted.  It  is  found  that  a  velocity  of  26  feet  per 
second  in  the  pipes  is  permissible  and  occasions  no  serious  loss 
of  head,  though  in  1891  the  velocity  did  not  generally  reach 
that  figure.  At  this  velocity  and  pressure  a  12 -inch  pipe  would 
carry  very  nearly  1000  h.p.  About  35  pounds  of  air  per  hour 
is  required  for  a  horse-power  when  heated  to  300°  F.  before 
admission.  The  heating  consumes  about  I  pound  of  coke  per 
hour  for  5  h.p. 

The  most  important  detail  of  the  whole  system  is  the  joints 
of  the  pipe.  Air-pipes  are  liable  to  greater  variation  of  tem- 
perature than  others,  and  rigid  joints  have  always  given  trouble. 
Cast-iron  pipes  have  been  mainly  used  at  Paris.  The  most 
satisfactory  joint  is  the  one  shown  at  Fig.  201.  The  pipes  are 
perfectly  plain,  having  no  bells,  spigots,  flanges,  or  other 
means  of  attachment.  In  joining  two  pipes  a  heavy  collar 
provided  with  bolt-holes  is  slipped  on  the  end  of  each  piece. 
Then  a  rubber  ring  is  slipped  on;  then  a  sleeve  is  applied 
embracing  both  pieces  of  pipe,  and  the  latter  are  brought 


THE  BIRMINGHAM  COMPRESSED-AIR  SYSTEM.       423 

nearly  together  but  not  into  contact.  Bolts  are  then  inserted 
and  the  nuts  turned  up  strongly,  compressing  the  rubber  rings 
against  the  ends  of  the  sleeve.  This  joint  admits  of  free 
expansion  and  contraction  as  well  as  some  deviation  from  a 
straight  line,  which  in  a  line  of  pipe  is  unavoidable.  The 


in 

T 

. 

=j 

-/ 

H 

-J-1- 

\H-       h—-4rfH J      j 


FIG.  201.  FIG.  20i«. 

leakage  of  these  joints  is  very  slight.  Prof.  Reidler*  gives  re- 
sults of  experiments  on  a  system  of  9000  yards  of  pipe  at  Paris, 
and  found  the  loss  from  leakage  3  per  cent.  The  system  of 
air-pipes  at  Offenbach, t  near  Frankfort-on-the-Main,  when 
under  a  pressure  of  6f  atmospheres  (about  100  pounds)  showed 
a  leakage  of  about  1.7  cubic  feet  air  per  hour  for  each  mile  of 
pipe.  This  consisted  of  13  ooo  feet  4-inch,  5000  feet  3-inch, 
and  5000  feet  i5  inch  pipe.  Prof.  Reidler  in  1891  was  of 
opinion  that,  under  conditions  then  existing  in  Paris,  motors  of 
ordinary  construction  could  utilize  80  per  cent,  and  with  some 
simple  and  obvious  improvements  100  per  cent  of  the  power 
expended  by  the  compressors,  always  assuming  the  expendi- 
ture of  a  small  quantity  of  fuel  in  heating  the  air. 

The  Birmingham  Compressed-air  System  was  commenced 
about  1886,  and  it  was  complete  and  in  operation  in  1890. 
Preliminary  to  this  installation  the  conditions  at  Birmingham 
affecting  such  an  enterprise  were  examined  by  Sir  F.  Bramwell 
and  Mr.  Percy  and  found  very  favorable.  This  city  contains 
an  immense  number  of  small  establishments  run  by  steam. 
The  small  engines  in  general  use  were  found  to  consume  coal 

*  London  Engineering,  March  13,  1891. 
f  Ibid.,  October,  1891. 


424  PNEUMATIC  TRANSMISSION. 

at  a  most  extravagant  rate — in  no  case  less  than  S£  pounds, 
and  in  some  cases  as  high  as  36  pounds  per  horse-power  per 
hour.  It  was  fairly  reasoned  that  such  users  would  find  great 
advantage  in  taking  their  power  from  the  air-mains  at  rates 
remunerative  to  the  company.  Compressing  engines  to  the 
extent  of  3000  h.p.  were  installed.  The  pressure  adopted  was 
45  pounds.  The  pipes  were  of  riveted  wrought  iron,  put 
together  with  lead  joints.  Prof.  A.  Lupton*  of  the  Yorkshire 
College,  Leeds,  stated  that  the  indicated  efficiency  of  the  motors 
at  Birmingham  \vas  73  per  cent  of  the  indicated  efficiency  of  the 
air-compressing  engines.  Great  trouble  was  always  experienced 
here  from  leakage.  It  is  stated  that  the  pressure  in  the  mains 
was  but  20  pounds,  instead  of  45  as 'intended.  This  would 
indicate  leakage  of  enormous  proportions.  This  company  t 
failed,  and  its  affairs  were  wound  up  in  1891.  If  the  statements 
as  to  leakage  and  loss  of  pressure  are  true,  this  would  suffi- 
ciently account  for  the  failure.  However  that  may  be,  it  cannot 
be  denied  that  the  Paris  enterprise  is  a  conspicuous  success  and 
demonstrates  the  commercial  feasibility  of  such  projects  when 
justified  by  existing  conditions  and  properly  conducted. 
Experience  at  Paris  and  Offenbach  justify  the  statement  that 
air  may  be  transmitted  through  pipes,  excluding  leakage,  at  a 
velocity  of  25  feet  per  second,  with  a  loss  of  not  more  than  1.5 
pounds  pressure  per  mile.  It  must  be  borne  in  mind  that  a 
loss  of  pressure  in  air  does  not  imply  a  proportional  loss  of 
power,  as  is  the  fact  in  case  of  water.  Loss  of  pressure  is 
accompanied  by  an  increase  of  volume.  Table  9  shows 
that  reducing  the  pressure  from  100  to  95,  i.e.,  5  per  cent, 
reduces  the  power  only  2.7  per  cent.  By  Table  1 1  it  would  be 
under  2  per  cent.  Both  these  results  are  theoretical ;  the  actual 
loss  would  be  between  the  two,  say  something  under  2.5  per 
cent.  We  may  say,  therefore,  that  the  loss  of  power  with  the 
above  velocity  need  not  exceed  i  per  cent  per  mile.  Another 
point  of  importance  is  this :  For  the  proper  regulation  of  the 

*  Meeting  of  British  Assoc.,  September,  1890. 
f  London  Engineering,  January  i,  1892. 


THE    TRONC.  425 

pressure  in  such  a  system  a  considerable  receiver  capacity  is 
necessary.  This  receiver  capacity  costs  no  more  in  the  form 
of  enlarged  pipes  than  in  the  form  of  separate  vessels. 

The  longest  air  transmission  in  America  is  at  the  Chapin 
Mine,  Iron  Mountain,  Michigan.  The  source  of  power  is  a 
waterfall.  There  is  one  pair  36  X  60  and  three  pairs  32  X  60  Rand 
compressors.  The  air  is  sent  3  miles  through  a  24-inch  pipe. 
The  pressure  at  the  compressors  is  60  pounds,  at  the  motors 
57|  to  58,  implying  a  loss  of  power  of  about  2  per  cent.  The 
air  being  used  mainly  underground,  it  is  not  practicable  to 
reheat  it.  The  pipe  is  24  inches  diameter,  of  ^-inch  sheet  iron, 
each  sheet  wide  enough  to  make  a  24-inch  pipe,  and  8  feet 
long,  single-riveted  on  all  joints.  The  pipe  is  put  together  in 
lengths  of  58  feet  with  riveted  flange-joints,  a  paper  gasket 
being  interposed  at  each  joint.  There  are  29  expansion-joints 
in  the  course  of  the  pipe,  each  admitting  a  movement  of  18 
inches.  The  pipe  rests  on  bents  or  trestles  58  feet  apart,  and 
is  provided  with  rollers  or  rocker  feet  so  that  it  accommodates 
itself  readily  to  changes  of  temperature.  These  facts  were 
communicated  by  Mr.  James  MacNaughton,  superintendent  of 
the  mine. 

As  already  mentioned,  grave  mechanical  difficulties  attend 
the  application  of  the  turbine  to  the  duty  of  compressing  air. 
Unless  a  number  of  compressors  are  driven  by  the  same  wheel, 
which  is  not  always  desirable,  a  heavy  fly-wheel  is  imperatively 
essential  to  economical  working.  Thhs  on  a  vertical  shaft  is 
generally  out  of  the  question;  and  on  a  horizontal  shaft,  which 
must  run  in  stuffing-boxes,  is  attended  with  difficulties. 
Moreover,  on  a  high  head  the  motion  of  the  wheel  becomes 
too  rapid  for  the  economical  working  of  the  air-compressor 
without  the  intervention  of  gearing.  For  these  reasons  the 
attention  of  engineers  is  often  directed  to  devices  for  compress- 
ing air  by  the  direct  action  of  water,  without  the  intervention 
of  water-wheels. 

The  Tronc,  formerly  used  for  creating  a  blast  for  iron- 
furnaces,  is  well  known  to  mechanicians.  A  column  of  water 


426  PNEUMATIC  TRANSMISSION. 

descending  through  a  vertical  pipe  carries  air  with  it  and 
deposits  the  same  in  a  receiver,  under  a  pressure  somewhat  less 
than  that  due  the  head.  It  can  under  no  condition  bring  the 
air  to  a  pressure  greater  than  that  due  the  head. 

The  Ram. — By  alternately  establishing  and  interrupting 
the  movement  of  water  in  a  long  pipe,  the  momentum  of  the 
latter,  acting  upon  a  confined  mass  of  air,  will  bring  it  to  a 
pressure  far  exceeding  that  due  the  head  acting  on  the  pipe. 
A  pipe  i  square  foot  in  cross-section  and  a  mile  in  length  con- 
tains 330  ooo  pounds  of  water.  Such  a  column  being  in  motion 
with  a  velocity  of  4  feet  per  second  would  in  coming  to  rest 
give  out  energy  to  the  amount  of  some  80  ooo  foot-pounds — 
sufficient,  according  to  Table  9,  to  bring  1.5  pounds  of  air  to  a 
tension  of  100  pounds.  The  head  acting  on  the  pipe  need  not 
be  more  than  20  or  30  feet. 

The  simplest  application  of  this  principle  is  in  the  well- 
known  hydraulic  ram  of  Montgolfier,  which  at  each  stoppage 
compresses  air  in  a  chamber,  and  the  latter  by  its  expansion 
forces  water  to  a  height  above  the  source  of  supply.  Of  this 
character  was  the  first  air-compressor  used  at  the  tunnel  of 
Mont  Cenis,  designed  by  M.  Sommeiller,  to  furnish  air  for  the 
drills.  This,  on  account  of  the  high  velocity  required  and  the 
friction  in  the  line  of  pipe,  was  found  to  be  wasteful  and,  from 
the  violence  of  its  action,  difficult  and  expensive  to  keep  in 
repair.  It  was  discarded  and  replaced  by  a  turbine  driving 
piston  compressors. 

An  English  engineer,  Mr.  E.  D.  Pearsall,  has  devoted 
himself  to  the  improvement  of  the  Sommeiller  compressor. 
He  avoids  the  violence  of  the  former  action  by  a  cylinder-valve 
for  arresting  the  motion.  This  is  operated  by  a  small  air- 
motor.  This  modification  is  said  to  work  very  well,  having 
shown  on  a  small  scale,  as  is  claimed,  an  efficiency  of  80  per 
cent. 

Fig.  215  shows  a  method  of  compressing  air  by  the  direct 
action  of  water  without  the  use  of  mechanism  of  any  kind. 
This  method  was  patented  .by  the  writer  in  1878,  and  has 


THE  RAM.  427 

received  some  application.  It  is  founded  upon  the  familiar 
observation  that  water  thrown  into  commotion  breaks  into  foam 
and  becomes  impregnated  with  minute  air-bubbles,  and  upon 
the  further  fact  that  these  bubbles  rise  through  water  with  a 
very  moderate  velocity  and,  in  a  descending  current,  are  carried 
downward  cftid  subjected  to  a  pressure  conformable  to  the  depth. 
Figs.  215  and  215^  show  the  arrangement  for  applying  these 
principles  on  a  practical  scale.  It  assumes  a  fall  created  by  a 
dam  on  a  running  stream.  It  assumes,  what  is  generally  the 
fact  at  a  fall  or  rapid,  a  rock  formation  at  no  great  depth.  On 
the  up-stream  side  of  the  dam  a  vertical  shaft  descends  into  the 
ground  to  a  depth  corresponding  to  the  required  pressure. 
At  that  depth  its  direction  changes  to  horizontal,  and  it  pursues 
this  course  to  a  point  below  the  dam,  where  it  joins  a  second 
vertical  shaft  opening  into  the  river.  Around  the  entrance  to 
the  shaft  a  masonry  structure  rises  to  the  elevation  of  the  dam 
or  something  more,  and  is  provided  with  means  for  controlling 
the  influx.  Over  the  horizontal  passage  a  capacious  chamber 
is  formed,  provided  with  an  impervious  lining.  The  trans- 
mission-pipe leads  from  this  chamber.  Water  entering  the 
descending  shaft  from  different  directions  meets  with  a  high 
relative  velocity,  and  is  thrown  into  violent  commotion  which 
impregnates  it  with  air-bubbles  of  a  minute  and  very  uniform 
size.  Such  bubbles  tend  to  rise  with  a  velocity  of  not  more 
than  i  foot  per  second,  and  the  descending  current  being  4  feet 
or  more,  they  are  carried  downward.  In  the  horizontal  part  of 
the  passage  the  air  is  free  to  rise  and  accordingly  enters  the 
air-chamber  and  there  accumulates  under  a  pressure  correspond- 
ing to  the  depth  of  the  surface  of  water  in  the  chamber  below 
the  surface  in  the  stream.  The  water  divested  of  its  burden  of 
air  pursues  its  course  and,  rising  through  the  ascending  shaft, 
joins  the  river. 

The  compression  in  this  method  takes  place  isothermally 
and  avoids  one  principal  source  of  loss  in  machine  compressors. 
The  losses  inherent  in  the  method  are: 

i .   The  head  expended  in  impregnating  the  water  with  air, 


428  PNEUMATIC   TRANSMISSION. 

which  includes  the  head  due  the  initial  velocity.  A  fall  of 
i  foot  in  entering  the  shaft  brings  in  the  water  from  both  sides 
with  a  velocity  of  8  feet  per  second,  and  these  two  currents 
meet  with  a  relative  velocity  of  16  feet  per  second,  which 
creates  a  sufficient  commotion. 

2.  A  loss  which  may  be  called  the  slip  due  to' the  velocity 
with  which  the  bubbles  tend  to  rise.  It  is  obvious  that  the  rise 
of  the  bubbles  during  the  descent  of  the  water  is  a  lost  motion, 
to  be  deducted  from  the  efficiency  of  the  system. 

In  addition  there  is  the  head  consumed  by  the  friction  in 
the  channels.  An  extended  series  of  experiments  *  on  this 
method  was  made  by  the  author  at  Minneapolis,  Minn.,  in 
1880,  the  fair  deduction  from  which  was  that  on  a  practical 
scale  and  in  a  plant  intelligently  designed  and  carefully 
executed  as  much  as  75  per  cent  of  the  absolute  power  of  the 
water  would  be  represented  in  the  air  compressed. 

A  method  of  compressing  air  on  these  principles  has  been 
in  use  for  several  years  at  the  outlet  of  Magog  Lake  in  the 
province  of  Quebec  (Fig.  216).  In  this  case  a  combination  of 
pipes  has  been  used  for  introducing  the  air.t  Some  62  per  cent 
was  the  greatest  efficiency  found  in  this  apparatus.  Even  this 
low  result  compares  favorably  with  what  could  be  expected 
from  water-wheels,  where,  reckoned  on  the  total  fall,  we  could 
not  count  on  an  efficiency  of  more  than  75  in  the  water-wheel, 
and  say  at  best  80  in  the  compressor,  giving  for  the  energy 
represented  by  the  compressed  air  .75  X  -80  =  60  per  cent  of 
the  total  absolute  power  of  the  water.  This  method  is  more 
fully  considered  under  the  head  of  Power-houses. 

*See  Journal  of  the  Franklin  Institute,  September,  1880. 
\  London  Society  of  Engineers,  June,  1897. 


CHAPTER   XXI. 
TRANSMISSION   BY   ELECTRIC  CURRENT 

IT  was  discovered  by  Faraday  in  1831  that  an  electric 
conductor  crossing  a  magnetic  field,  i.e.,  the  space  in  the 
immediate  vicinity  of  a  powerful  magnet,  undergoes  a  certain 
attraction  or  repulsion ;  that  when  moved  against  the  repul- 
sive force  it  generates  a  current  of  electricity;  and  that  when 
supplied  with  electric  current  and  allowed  to  move  in  obedience 
to  the  force,  it  may  be  made  to  generate  mechanical  energy. 
This  principle  has  received  immense  application  in  the  last 
twenty  years  in  the  form  of  electric  generators  and  motors. 
An  enormous  development  of  the  science  of  electricity  has  taken 
place  within  that  period.  It  forms  the  subject  of  lectures  and 
periodical  literature,  of  special  courses  in  industrial  schools,  and 
of  books  that  cannot  be  numbered  for  multitude.  It  is  not 
intended  in  this  work  to  enter  into  the  science  of  electricity  or 
the  construction  of  electric  machines,  beyond  a  brief  reference 
to  such  general  principles  as  relate  to  the  transmission  of 
power. 

Analogy  between  Electric  and  Other  Modes  of  Transmis- 
sion.— In  transmission  by  fluids  under  pressure,  the  elements 
of  the  power  are  the  pressure  and  the  rate  of  flow,  i.e.,  I  cubic 
foot  of  water  per  second  under  a  head  of  9  feet  is  very  closely 
a  theoretical  horse-power,  namely,  a  horse-power  neglecting 
unavoidable  losses  in  application.  Practically  I  cubic  foot  per 
second  under  a  head  of  1 1  or  1 2  feet  is  a  horse-power,  and  if  h 
represent  the  head  in  feet,  and  q  the  flow  in  cubic  feet  per 
second,  the  power  may  be  represented  by  the  product  hq.  In 
electric  transmission  we  deal  with  two  analogous  elements, 

429 


43°  TRANSMISSION  BY  ELECTRIC  CURRENT. 

viz.,  the  electromotive  force  or  potential  E  in  volts,  and  the 
current  /  expressed  in  amperes,  the  power  being  proportional 
to  the  product  El.  Thus,  neglecting  losses  in  application,  a 
flow  of  20  cubic  feet  of  water  per  second  under  a  head  of  1 8 

feet  would  represent  about  -  --  =  40  h.p.      A  current  of 

/  =  40   amperes   under   a  potential  of  E  =  500  volts    would 

represent — >= ^ =   26.8    h.p.       The    product   El 

740  740 

represents  the  power  of  a  current  of  electricity  in  units  called 
watts,  a  watt  being  I  ampere  of  current  under  i  volt  of  poten- 
tial, and  746  watts  being  equal  to  a  horse-power.  An  analogous 
term  is  found  in  leases  of  water-power,  viz.,  the  mill-power, 
which  is  such  a  quantity  of  water-power  that  the  product  of  the 
quantity  of  water  in  cubic  feet  per  second  by  the  fall  in  feet 
shall  equal  a  certain  fixed  sum.  Oliver  Evans,*  one  of  the 
earliest  water-power  engineers  in  the  United  States,  introduced 
the  term  cubock  in  the  sense  of  the  product  of  cubic  feet  per 
second  by  feet  of  head,  i.e.,  10  cubic,  feet  per  second  under  12 
feet  head  =120  cubocks.  This  term  was  the  exact  analogue 
of  the  watt.  In  fluid  transmission  we  sometimes  use  the 
symbols  h  and  P  to  mean,  not  the  absolute  head  or  pressure 
in  a  pipe  or  channel,  but  the  loss  of  head,  i.e.,  the  head  or 
pressure  expended  in  maintaining  the  flow  in  a  certain  length 
of  the  pipe  or  channel.  Likewise  in  electricity,  the  symbol  E 
is  sometimes  used  to  designate,  not  the  absolute  potential  of 
the  current,  but  the  loss  of  potential  in  a  foot,  a  mile,  etc.,  of 
the  conductor.  In  each  case  the  proper  use  of  the  symbol  is 
always  clear  from  the  context,  and  the  apparent  confusion 
occasions  no  misapprehension  to  those  familiar  with  such  com- 
putations. 

The  power  transmissible  in  a  fluid  form  depends  upon  the 
nature  of  the  channel  of  transmission,  and  the  more  difficult 
the  passage  the  greater  the  quantity  of  power  consumed  in 

*  Millwright's  Guide.      Philadelphia,  1848. 


EXPANSION.  431 

transmission.  Electric  transmission  is  perfectly  analogous. 
The  channels  of  transmission  are  metallic  wires.  The  pressure 
or  voltage  consumed  in  transmission  is  directly  as  the  length 
and  inversely  as  the  cross-section.  The  lost  power  is  in  both 
cases  transformed  into  heat,  though  in  the  case  of  electricity 
the  heat  becomes  very  sensible  on  account  of  the  comparatively 
small  size  of  the  conductor,  while  in  air  it  is  but  slightly  sen- 
sible, and  in  water  entirely  insensible. 

A  quantity  q  of  compressed  air  under  pressure  P  may  be 
changed  into  a  greater  volume  under  a  less  pressure  or  a 
smaller  volume  under  a  greater  pressure,  representing  the  same 
amount  of  power  in  each  case.*  A  quantity  q  of  water  under 
the  head  h  may,  neglecting  losses,  be  employed  to  pump  a 

greater  quantity  aq  to   a  height  -  or  a  smaller  quantity  --  to  a 

height  ah,  the  result  representing,  in  each  case,  the  same 
power.  In  like  manner  an  electric  current  /  at  potential  E 
may,  by  certain  devices  called  transformers,  be  changed  into 

a  current  —  at  potental  aE  or  a  current  al  at  potental  — ;   in 
a  a' 

either  case  representing,  unavoidable  losses  excepted,  the  same 
amount  of  power.  The  device  which  diminishes  the  potential 
and  increases  the  current  is  called  a  step-down  transformer; 
that  giving  the  reverse  effect,  a  step-up  transformer.  It  is 
through  these  devices  that  electric  transmission  to  long  dis- 
tances is  possible. 

Expansion.  —  Unlike  elastic  fluids,  electricity  does  not 
develop  power  in  passing  from  high  to  low  potential,  or  absorb 
power  in  the  reverse  transformation.  The  energy  derived  from 
expansion  of  air  has  no  analogue  in  electricity. 

*This  statement  might  appear  contradictory,  as  a  quantity  q  of  air  at 
volume  v,  and  pressure  P,  would  develop  power  in  passing  to  volume  v? 
and  pressure  Py;  but  if  air  passes  freely  from  PI  to  P,,  it  will  develop  heat 
in  z>2,  which  preserves  the  power  unaltered.  Likewise  if  the  air  passes 
from  Vi  to  the  lesser  volume  v3  and  greater  pressure  P3,  the  power  of 
Psft,  omitting  losses  and  dissipation  of  heat,  is  exactly  equal  to  that  of 
P\v\  plus  the  power  expended  in  compressing  the  air  from  Pi  to  Pt. 


432 


TRANSMISSION  BY  ELECTRIC   CURRENT. 


Resistance  to  the  passage  of  the  current  follows  a  more 
simple  law  in  electric  conductors  than  in  pipes  and  channels. 
It  is  directly  as  the  length  of  the  conductor  traversed,  ordinarily 
called  the  circuit,  and  inversely  as  the  cross-section.  Resist- 
ance is  expressed  in  ohms,  the  relation  between  the  current, 
the  potential,  and  the  resistance  being  represented  by  the 

equation  E  =  RI,  whence  R  =  —,  which  means  that  a  differ- 
ence of  potential  of  i  volt,  in  a  circuit  whose  resistance  is 
i  ohm,  will  cause  a  current  of  I  ampere.  Resistance  varies 
greatly  in  different  substances.  In  some  it  is  so  great  that  the 
passage  of  the  current  under  any  attainable  difference  of  poten- 
tial is  practically  null.  Such  substances  are  used  as  insulators 
to  prevent  the  escape  of  electricity  from  conductors  at  their 
resting-points,  and  for  other  purposes.  Conductivity  is  the 
reciprocal  of  resistance,  high  conductivity  meaning  low  resist- 
ance. The  following  table,  borrowed  from  Unwin,  gives  the 
relative  conductivity  of  metals  susceptible  of  use  as  conductors.. 

TABLE   12.— COMPARISON    OF   ELECTRIC    CONDUCTORS. 


a 

b 

ab 

Material. 

Conduc- 
tivity. 

Density. 

Conduc- 
tivity of 

Tenacity, 
Tons  per 

Product  of 

Equal 

Square 

a  and  b. 

Weights. 

Inch. 

8  o 

*    08 

8n 

0Q 

1700 

Q     0 

1280 

16  ? 

•7     B 

18  8 

2 

Galvanized  iron  

14 

7-7 

16.1 

25 

423 
400 

8  o 

e8 

fiSn 

2    6 

188 

8  o 

28 

80 

o.y 
8    Q 

y/ 
go 

,, 

45 

8.9 

45 

49 

22OO 

26 

8    Q 

26 

The  tenacity  of  the  material  is  important  as  regards  the 
supports  of  the  wires ;  the  stronger  the  material  the  greater  the 
distances  allowable  between  the  supports.  The  tension  on  a 


RESISTANCE.  433 

wire  suspended  from  two  fixed  points  is  arrived  at  with  sufficient 
accuracy  for  this  purpose  in  the  following  manner.  Let  AB 
=:  /  be  the  distance  between  the  supports,  Fig.  202.  The 


c 
FIG.  202. 

deflection  d  is  small  compared  with  /,  and  the  curve  is  not  essen- 
tially different  from  a  parabola,  in  which  the  intersection  of  the 
tangents  C  is  at  the  distance  d  below  the  curve,  w  being  the 
weight  of  the  wire- per  foot,  the  total  weight  wl  may  be  supposed 
concentrated  at  C ',  causing  a  tension  E  on  the  tangents  equal 
to  that  on  the  wire  at  A  and  B.  Completing  the  parallelogram 
of  forces  we  have,  neglecting  the  difference  in  length  between 

BC  and  BE,  t  :  —  =  —  :  2et.     .-.  t  =  ^j.     Dividing  /  by  the 

cross-section  of  the  wire  gives  the  tension  per  square  inch  of 
metal. 

The  sixth  column  of  the  table  shows  the  two  quali-ties  of  con- 
ductivity and  tenacity  in  combination,  in  which  respect  hard 
copper  heads  the  list,  though  silicon  bronze  follows  very 
closely.  As  regards  conductivity  per  unit  of  weight  nothing 
approaches  aluminium.  The  ores  of  this  metal  in  the  form  of 
oxides  exist  in  great  abundance  in  all  parts  of  the  world,  and 
modern  methods  of  metallurgy  are  constantly  tending  toward 
its  cheaper  production.  It  is  very  probable  that  it  will  even- 
tually become  the  most  available  material  for  electric  con- 
ductors. 

Table  13  gives  numbers,  sizes  resistances,  etc.,  for  copper 
wire.  It  can  be  used  for  wire  of  other  metals  by  the  aid  of 
Table  12.  The  first  column  gives  the  designation  of  the  wire, 
following  the  system  of  Brown  &  Sharpe  of  Providence,  R.  I. 
After  the  numbers  and  sizes  were  established  it  became  neces- 
sary to  find  designations  for  sizes  larger  than  No  I ,  which  led 


434 


TRANSMISSION  BY  ELECTRIC  CURRENT. 


TABLE  13.— DIMENSIONS  AND   RESISTANCES  OF  PURE  COPPER 
WIRE. 


American 
Gauge, 
Brown  & 
Sharpe's 
Numbers. 

2 

Diameter  in 

Mills. 

3 

Area  of  Cross- 
>ection  Circu- 
lar Mills 
=  Diameter1. 

4                        5 
Weight  and  Length. 

6                        7 
Resistance  at  75°  F. 

Pounds  per 
1000  Feet. 

Feet  per 
Pound. 

Ohms  per 
1000  Feet. 

Feet  per 
Ohm. 

oooo 

460 

211  600 

639-33 

1.56            .04906 

20383 

000 

409.64 

167  80S 

507.01 

1-97 

.06186 

16  165 

CO 

364.80 

I33079-40 

402.09 

2.49 

.07801 

12820 

0 

324-05 

105  592-50 

319.04 

3-13 

.09831 

10409 

I 

289.30 

83694.20 

252.88 

3-95 

.12404 

8062 

2 

257-63 

'     663/3.00 

2.0.54 

4.99 

.15640 

6394 

3 

229.42 

52  634.00 

159-03 

6.29 

•19723 

5070 

4 

204.31 

41  742.00 

126.12 

7-93 

.  24869 

4021 

5 

181.94 

33  102.  oo 

100.  OI 

IO.CO 

.31361 

3189 

6 

162.02 

26250.50 

79-32 

.12.61 

•39546 

2529 

7 

144.28 

20816.00 

62.90 

15.90 

.49871 

2005 

8 

128.49 

16  509.00 

49.88 

20.05 

.62881 

1590 

9 

114-43 

13  594.00 

39-56 

25.28 

.79281 

I  26l 

10 

101.89 

10  381.00 

31-37 

31-38 

I.  00000 

I  OOO 

ii 

90.742 

8234.00 

24.88 

40.20 

I  .  2607 

793-2 

12 

80-808 

6529-90 

19-73 

50.69 

1.5898 

629.0 

13 

71.961 

5  178-40 

15.65 

63.91 

2.0047 

498.8 

M 

64.084 

4  106.80 

12.41 

80.59 

2.5908 

386.0 

15 

57-068 

3256.70 

9.84 

101.63 

3-1150 

321.0 

16 

50.820 

2582.90 

7.81 

128.14 

4.0191 

248.8 

I? 

45.257           2048-20 

6.  19 

161.59 

5.0683 

197-3 

18 

40.303 

1624.30 

4.91 

203.76 

6.3911 

156-5 

19 

35-39° 

'     1252.40 

3-78 

264.26 

8.2889 

120.6 

20 

31-961 

I  021.50 

3-09 

324-00 

10.163 

98.40 

21 

28.462 

810-10 

2-45 

408.56 

12.815 

78.04 

22 

25-347 

642.70 

1.94 

515.15 

16.152 

61.91 

23 

22.571 

509.45 

1-54 

649.66 

20-377 

49-09 

24 

20.  TOO 

404.01 

1.22 

819.21 

25-695 

39.92 

25 

17.900 

320.40 

°-97 

1032.96 

32.400 

30.86 

26 

15-940 

254.01 

-77 

I  302.61 

40.868 

24-47 

27 

I4-I95 

201  .  5O 

.61 

I  642.55 

5I-5I9 

19.41 

28 

12.641 

159-79 

.48 

2  071.22 

64.966 

15-39 

29 

11.257 

126.72 

•38 

2611.82 

81.921 

12.21 

30 

IO.O25 

IO0.50 

•3° 

3293-97 

103.30 

9.68 

31 

8.928 

79-71 

.24 

4152.22 

127.27 

7.86 

32 

7-950 

63.20 

.19 

5236.66 

164.26 

6.09 

33 

7.080 

50.13 

•  15 

6  602.71 

207.08 

4-83 

34 

6.304 

39-74 

.12 

8328.30    261.23 

3-83 

35 

5.614 

3i  52 

.10 

10501.35    329-35 

3-04 

36 

5-OOO 

25.00 

.08 

13238.83    415-24 

2.41 

37 

4-453 

19-83 

.06 

16  691.06 

523.76 

I.gi 

38 

3-965 

15-72 

.05 

20854.65 

660.37 

1-52 

39 

3-531 

12.47 

.04 

26  302.23 

832.48 

I.  2O 

40 

3-144 

9.89 

•°3 

33I75.9-4 

1049.7 

0-95 

POTENTIAL  IN   TRANSMISSION.  435 

to  the  symbols  o,  oo,  etc.  The  second  column  gives  the 
diameter  in  mills,  i.e.,  in  thousandths  of  an  inch.  The  third 
gives  the  equivalent  number  of  wires  of  I  mill  diameter,  i.e.,  a 
No.  i  wire  is  equivalent  to  83  694  wires  of  I  mill  diameter. 
The  remaining  columns  explain  themselves.  The  resistance 
varies  materially  with  the  temperature.  It  is  given  here  for  a 
temperature  of  75°  F. 

Potential  in  Transmission.  —  We  are  now  in  a  position  to 
understand  the  enormous  advantage  of  high  tensions  in  electric 
transmission.  Let  it  be  required  to  find  the  loss  of  potential  in 
sending  20  h.p.  over  a  line  of  No.  I  copper  wire  10  miles  long, 
with  a  potential  of  550  volts  at  the  receiving  end,  which  is 
about  the  voltage  required  for  street-cars.  Such  a  line  has, 
by  the  table,  a  resistance  of  0.12404  X  5.280  X  10  —  6.55 
ohms.  The  current  at  the  receiving  end  must  be  such  that 

14  920 
El  :=  20  X  746  =  14  920  watts.     Whence  7  =  -  =  27.  i 

amperes.  To  prevent  confusion  let  e  represent  the  electro- 
motive force  required  to  move  the  current.  Then 

^  =  6.55  X  27.1  =  177.5. 
The  loss  in  the  wire  therefore  is 

177.1;  volts  =  --  ;  —  -  --  —  24.0  per  cent  of  the  power 

550+  177-5 
delivered  to  the  wire. 

Again,  let  it  be  required  to  s£nd  10  h.p.  =•  7460  watts  over 
the  same  line  at  a  potential  of  1  20,  which  is  suitable  for  electric 

lighting.      Here  we  must  have  /=  —  -  =  62.2  amperes,  and 

e  —  62.2  X  6.55  =  407.  That  is  to  say,  not  more  than  23  per 
cent  of  the  power  imparted  to  the  wire  would  be  delivered  at 
the  receiving  end. 

Now  assume  the  transmission  of  1000  h.p.  over  the  same 
line  at  a  potential  of  1  5  ooo  volts.  In  this  case  El  =  746  ooo, 


7=  =  49-  7  amperes,  e  =  Rf  =  6.5$  X  49-7  =  325-5. 


436 


TRANSMISSION  BY  ELECTRIC  CURRENT. 


and  the  loss  in  the  wire  is 


325-5 
1S  325. 


=  a  little  over  2  per  cent. 


Of  course  this  is  not  the  only  loss  in  such  a  transmission  ;  there 
are  liable  to  be  losses  from  defective  insulation,  and  unavoidable 
losses  in  the  transformers  which  wholly  overshadow  the  above. 
Moreover,  the  above  resistance  does  not  include  the  return 
wire.  The  aggregate  loss  is  less  influenced  by  the  length  of 
line  than  by  other  factors. 

Temperature.  —  As  already  mentioned,  the  resistance  of 
electric  conductors  is  affected  by  temperature.  Table  14,  given 
by  Houston  on  the  authority  of  Latimer  Clark,  shows  the  effect 

TABLE    14.'—  RESISTANCE   AND    CONDUCTIVITY   OF    PURE 
COPPER    AT    DIFFERENT   TEMPERATURES. 


Temperature 
Centigrade. 

Resistance. 

Conductivity. 

Temperature 
Centigrade. 

Resistance. 

Conductivity. 

0° 

.OOOOO 

I  .  OOOOO 

1  6° 

.06168 

.94190 

I 

.00381 

.99624 

17 

•06563 

.93841 

2 

.00756 

.99250 

18 

.06959 

•93494 

3 

.01135 

.98878 

19 

.07356 

•93148 

4 

•OI5I5 

.98508 

20 

.07742 

.92814 

5 

.01896 

.98139 

21 

.08164 

.92452 

6 

.02280 

•97771 

22 

•08553 

.92121 

7 

.02663 

.97406 

23 

.08954 

.91782 

8 

.  03048 

•97042 

24 

•09365 

.91445 

9 

•03435 

.96679 

25 

•09763 

.91110 

10 

.03822 

.96319 

26 

.  10161 

.90776 

ii 

.04199 

•95970 

27 

.10567 

.90443 

12 

•04599 

.95603 

28 

.119/2 

•90113 

13 

.04990 

•95247 

29 

.11382 

.89784 

14 

.  05406 

.94893 

30 

.  11782 

•89457 

15 

•05774 

•94541  ' 

of  rise  of  temperature  upon  resistance  and  conductivity  of  pure 
copper,  up  to  30°  C.  =  86°  F.  It  will  be  noticed  that  at  the 
latter  temperature  the  resistance  is  about  1 2  per  cent  greater 
than  at  o°  C.  =  32°  F.,  so  that  cold  weather  is  more  favorat ' 
to  transmission  than  warm.  A  current  traversing  a  conduct*  i 
imparts  heat  to  it  at  the  rate  of  i  British  thermal  unit  for  every 
1058  watts  *  of  energy  consumed  in  resistance.  The  perma- 


*  This   is  S.  P.  Thompson's  figure, 
make  it  1057.—].  P.  F. 


Electric  Machinery,  1892,  p.  427. 


EFFICIENCY  OF  ELECTRIC   TRANSMISSION.  437 

nent  temperature  of  the  wire  will  depend  upon  the  rapidity  with 
which  the  heat  is  dissipated.  In  computations  relative  to 
transmission  strict  accuracy  would  require  us  to  take  account 
of  the  effect  of  this  heating  upon  the  resistance ;  but  we  cannot 
here  go  into  these  refinements. 

A  soft  copper  wire  I  mill  diameter,  I  foot  long,  called 
i  "mill-foot,"  at  10.22°  C.  =50.4°  F.,  has  the  standard 
resistance  of  exactly  10  legal  ohms.  At  15°.  56  C.  or  59°. 9  F. 
it  has  a  resistance  of  10.20  legal  ohms,  and  at  23°. 9  C.  or 
75°  F.  10.53  legal  ohms. 

Efficiency  of  Electric  Transmission.— One  of  the  earliest 
attempts  at  long-distance  transmission  was  made  under  direc- 
tion of  Marcel  Duprez  in  1882.  This  was  from  Meisbach  to 
Munich,  a  distance  of  34  miles,  on  the  occasion  of  an  industrial 
exhibition  at  the  latter  place.  A  double  line  of  telegraph-wire 
was  used  having  a  resistance  of  950  ohms.  The  potential  was 
2700  volts,  and  the  net  efficiency  of  the  transmission,  as  stated 
by  Professor  Von  Beetz,  president  of  the  exhibition,  was  32 
per  cent.  This  is,  no  doubt,  as  high  as  could  have  been 
expected  in  the  state  of  the  art  then  existing.  In  a  later 
experiment  by  the  same  electrician,  viz.,  in  1886,  power  was 
transmitted  between  Creil  and  Paris,*  a  distance  of  36  miles, 
with  a  voltage  of  6000  and  an  efficiency  of  45  per  cent. 
M.  Fontaine,  about  1886,  transmitted  some  50  h.p.  under  a 
voltage  of  6000  with  an  efficiency  of  52  per  cent.  These  suc- 
cessive results  very  clearly  show  the  progressive  development 
and  perfecting  of  methods.  In  1887  power  was  transmitted 
between  Kreigstetten  and  Solothurn,t  through  a  conductor  of 
9.23  ohms  resistance,  with  a  net  efficiency  of  74.7  per  cent. 

At  Steyermuhle  *  in  Tyrol,  in  1890,  some  8  h.p.  was 
transmitted  a  short  distance — less  than  half  a  mile — with  an 
efficiency  of  80.6  per  cent.  In  this  and  all  the  preceding 
cases,  the  power  applied  to  the  line  as  well  as  that  delivered 

*  Electrician,  1886,  xvn.  318. 

-    %  f  Journal  Soc.   Telegraph  Engineers,  i88S,  XVII.  337. 

\  Electrotechnische  Zeitschrift,  1890,  XI.  II. 


438  TRANSMISSION  BY  ELECTRIC  CURRENT. 

by  it  was  measured  by  brake  or  dynamometer.  78  per  cent  is 
the  efficiency  claimed  for  the  transmission  from  the  turbines  to 
the  factories  at  Schaffhausen,  a  distance  of  some  750  yards. 
This,  is  about  500  h.p.  sent  over  the  wires  at  624  volts. 

In  1891  the  principles  of  electric  transmission  were  fully 
understood  and  the  methods  developed  to  a  degree  not 
materially  exceeded  since  that  date.  In  this  year,  on  the 
occasion  of  an  electric  exhibition  at  Frankfort,  Germany,  power 
was  transmitted  from  a  turbine  located  at  Lauffen,  on  the 
Neckar,  to  Frankfort,  and  there  applied  to  electric  lighting  and 
other  purposes.  This  distance  is  stated  to  be  175  kilometers, 
about  109  miles.  A  line  consisting  of  three  bare  copper  wires, 
about  No.  6  B.  &  S.  gauge,  was  carried  on  tall  poles  from 
Lauffen  to  Frankfort.  It  is  stated  that  10000  porcelain 
insulators  were  used,  indicating  some  3300  poles,  being  at  the 
rate  of  30  to  the  mile.  The  turbine  at  Lauffen  drove  a  3 -phase 
alternator  capable  of  giving  three  currents  of  about  1400 
amperes  at  50  volts.  These  were  delivered  to  a  step-up  trans- 
former of  a  ratio  of  I  to  160.  The  current  went  over  the  line 
at  from  12  ooo  to  25  ooo  volts.  At  Frankfort  it  was  delivered 
to  a  step-down  transformer  and  converted  to  60  volts  to  supply 
either  lamps  or  3-phase  motors.  Table  1 5  *  gives  the  power 
taken  from  the  turbine  and  the  losses  in  the  several  elements  of 
the  system.  The  average  efficiency  of  the  system  is  73.3  per 
cent  according  to  these  figures,  but  it  is  given  by  S.  P.  Thomp- 
son as  72,  possibly  on  more  reliable  data.  The  latter  is  a  very 
gratifying  result  and  probably  could  not  be  exceeded  in  prac- 
tice. Supposing  the  turbine  to  give  75  per  cent  of  the  gross 
power  of  the  water,  this  would  indicate  .72  X  -75  =  54  per 
cent  of  the  water-power  transmitted  a  distance  of  109.  miles. 

These  tests  were  made  by  a  jury  of  experts  under  direction 
of  Prof.  H.  F.  Weber,  and  may  be  presumed  correct.  They 
are  especially  valuable  for  the  reason  that  disinterested  state- 
ments of  efficiency  are  seldom  met  with.  Men  assuming  to 

*  These  figures  are  taken  from  the  Electric  World  of  July  2,  1892. 


EFFICIENCY   OF  ELECTRIC   TRANSMISSION. 


439 


TABLE  15.— TRANSMISSION  FROM  LAUFFEN  TO  FRANKFORT, 
POWER  IN  H.P.  DELIVERED  AT  DIFFERENT  POINTS  OF 
THE  LINE. 


Number. 

By  Turbine. 

By  Dynamo. 

By 

Step-up 
Trans- 
former. 

At 
Step-down 
Trans- 
former. 

To  Lamps. 

Net 
Efficiency. 

I 

78.2 

66.1 

6l.I 

58.O 

53-5 

0.684 

2 

99-3 

86.8 

81.5 

76.5 

71.4 

0.719 

3 

105.9 

93-3 

87.7 

81.7 

76-3 

0.720 

4 

105.9 

93-3 

87.7 

81.8 

76.4 

0.722 

5 

112.7 

IOO.I 

94-5 

87.6 

82.2 

0.729 

6 

117.6 

104.9 

99.2 

91.7 

86.2 

0-733 

7 

120.9 

108.1 

102.4 

91-5 

89-5 

0.740 

8 

121.  I 

108.3 

IO2.6 

95-o 

89.4 

0.738 

9 

127.0 

114.4 

108.7 

100.7 

95-1 

0.749 

10 

127-5 

114.8 

109.  o 

100.9 

95-3 

0-747 

ii 

I5I.8 

I39-I 

132.8 

120.O 

114.0 

0-751 

12 

I5I-7 

139  o 

132.7 

I2O.2 

114.2 

0-753 

13 

189.2 

177.0 

169.9 

145-3 

138.9 

0.732 

14 

igO.O 

177-3 

170.3 

145-3 

138.9 

0.731 

15 

190.7 

177.9 

170.8 

145-3 

138.9 

0.728 

16 

194.7 

182.2 

175.1 

150.7 

144.2 

0.741 

17 

197.4 

184.8 

177.6 

152.4 

145.8 

0-739 

be  electricians  often  state  the  efficiency  of  transformers  at  97 
and  even  99  per  cent.  The  Engineering  News,  vol.  XXXIV. 
p.  256,  estimates  the  loss  in  transmission  of  power  generated 
by  a  steam-engine  and  sent  over  a  line  some  20  miles  in  length 
as  follows,  the  indicated  power  of  the  engine  being  taken  as 
unity: 


Efficiency  of  engine 0.92 

"  "  belting  and  jack-shaft.  0.90 

"  "dynamo 0.92 

"  "  step-up  transformer...  0.93 

"  "  line 0.88 

"  "  step-down  transformer.  0.93 

"  "  rotary  converter 0.84 

"  "  railway  circuit 0.90 

"  "  car  motors 0.85 


Efficiency  remaining 0.920 

"  "  0.828 

"  "  0.762 

....  0.709 
"  "  0.624 

0.581 

0.488 

"  "  0.438 

0.372 


That  is  to  say,  only  37  per  cent  of  the  indicated  power  of 
the. engine  becomes  available  in  propelling  cars.  In  the  case 
of  a  water-wheel  whose  efficiency  could  not  ordinarily  be  taken 
over  .75,  but  in  favorable  cases  .80,  the  percentage  of  power 


440  TRANSMISSION  BY  ELECTRIC  CURRENT. 

made  available  would  not  be  over  32,  understanding  that  this 
figure  refers  to  the  absolute  power  of  the  water  and  not  to  the 
power  rendered  by  the  wheel. 

On  the  other  hand  an  experiment  made  at  Ogden,  Utah, 
in  1898,  under  the  auspices  of  the  General  Electric  Company, 
and  conducted  by  its  agents,  in  which  current  was  transmitted 
73  miles  at  a  tension  of  30  ooo  volts,  is  stated  to  have  shown  a 
loss  of  only  9  per  cent,  including  4  per  cent  in  transformers. 

Systems  of  Electric  Transmission  in  America The 

mountainous  mining  regions  of  the  Pacific  slope  have  usually  a 
considerable  rainfall,  and  the  streams  are  fed  till  late  in  the 
season  by  melting  snows.  They  abound  in  steep  declivities, 
where  great  heads  can  be  obtained,  and  the  evaporation  is  not 
excessive.  There  is  great  demand  for  power  in  extracting  the 
precious  metals  from  auriferous  and  argentiferous  rock,  as  well 
as  for  electric  lighting  and  other  purposes,  and  coal  is  very 
expensive.  These  regions  have  offered  an  attractive  field  for 
electric  transmission. 

The  concentrating  works  of  the  Silverton  mines,  4  miles 
southeast  from  Silverton,*  Colorado,  were,  previous  to  1895^ 
run  by  steam.  The  works  being  12  300  feet  above  sea-level 
and  at  a  distance  from  railroad  communication,  accessible  only 
by  wagon-roads  through  a  very  rough  country,  the  coal  cost, 
delivered  to  furnace,  $8.75  per  ton,  entailing  an  expense  for 
this  item  of  about  $1000  per  month.  As  a  relief  from  this 
expense,  a  water-power  and  electric-transmission  plant  was 
adopted.  Water  was  conducted  from  a  point  on  the  Animas 
River,  above  Silverton,  in  a  3  X  4-foot  flume  about  9750  feet 
to  a  point  where  a  fall  of  180  feet  was  obtained.  The  flume 
rested  largely  on  trestles,  and  at  some  points  was  50  feet  or 
more  above  the  ground.  It  carried  some  40  cubic  feet  per 
second,  yielding,  on  the  above-mentioned  fall,  something  over 
600  h.p.  It  was  used  on  two  double-nozzle,  4-foot  Pelton 
wheels,  belted  to  two  I5O-K.W.  General  Electric  Company's 

*  Engineering  News,  vol.  XXXIV.  p.  114. 


SYSTEMS   OF  ELECTRIC   TRANSMISSION.  441 

3-phase  generators,  producing  a  current  of  2500  volts.  The 
current  is  transmitted  3  miles  over  an  exceedingly  rugged 
country  by  bare  copper  wires,  No.  36.  &  S.,  one  for  each  of 
the  3-phase  circuits. 

At  Fresno,*  Cal.,  power  is  received  from  the  north  fork  of 
the  San  Joaquin  River,  over  40  miles  distant.  The  water  is 
conducted  in  a  canal  about  7  miles  to  a  reservoir.  Thence  it 
is  conveyed  in  a  steel  pipe  20  to  24  inches  diameter  to  the 
power-house,  a  distance  of  over  4000  feet,  where  it  is  used  on 
Pelton  wheels  under  the  enormous  head  of  1400  feet.  These 
wheels  are  57  inches  diameter  and  make  600  revolutions  per 
minute,  developing  500  h.p.  each.  A  separate  wheel  is  "used 
for  the  exciters  of  the  dynamos.  The  current  is  generated  at 
700  volts  and  raised  by  transformers  to  1 1  200  volts  for  trans- 
mission to  Fresno,  where  it  arrives  at  a  voltage  of  10000,  the 
distance  being  35  miles.  It  is  said  that  75  per  cent  of  the 
current  generated  by  the  wheels  reaches  the  switchboard  at 
Fresno.  The  pipe  leading  from  the  reservoir  to  the  power- 
house is  \  inch  thick  at  the  former  point  and  -f  at  the  latter. 
In  case  of  a  breach  of  the  pipe  a  vacuum  would  be  created  near 
the  influx,  and  for  this  reason  a  series  of  valves  are  inserted 
opening  inwards  to  let  in  the  air,  in  such  an  event,  and  prevent 
the  collapse  of  the  pipe. 

Power  t  is  transmitted  from  the  American  River  near 
Folsom,  Cal.,  to  Sacramento,  a  distance  of  24  miles.  The 
current  is  generated  at  800  volts  and  raised  for  transmission  to 
1 1  ooo.  The  line  is  in  duplicate.  The  loss  in  the  line  is 
stated  as  7.5  per  cent  with  3000  h.p. 

The  longest  transmission  in  America  and  probably  the 
longest  in  the  world  now  in  practical  operation,  the  Frankfort- 
Lauffen  system  being  merely  an  experiment,  is  the  installation 
of  the  Southern  California  Power  Company,  who  develop  some 
4000  h.p.  at  Santa  Ana  Canyon,  near  Redlands,  and  transmit 
it  to  Lor>  Angeles,:}:  a  distance  of  80  miles.  A  head  of  750 

*  Engineering  News,  vol.  xxxvi.  pp.  12,  225. 

f  Ibid.,  vol.  XXXIII.  p.  243. 

\  Communicated  by  General  Electric  Co. 


442  TRANSMISSION  BY  ELECTRIC  CURRENT. 

feet  is  obtained  at  the  canyon,  which  is  used  on  Pelton  wheels. 
These  give  motion  to  four  75O-K.W.  dynamos,  coupled  direct 
to  the  wheel-shafts  and  running  300  revolutions  per  minute. 
The  current  is  delivered  at  750  volts  and  transformed  to 
33  ooo  for  transmission.  The  voltage  is  stepped  down  by 
rotary  transformers  for  railways,  and  by  static  transformers  for 
light  and  power. 

The  highest  voltage  known  to  be  used  in  transmission  is  in 
the  line  of  the  Telluride  Power  Transmission  Company  at 
Provo,*  Utah,  which  transmits  2000  h.p.  a  distance  of  55 
miles  at  40  ooo  volts. 

In  concluding  the  subject  of  transmission  this  remark 
appears  pertinent.  The  older  manufacturing  cities  are  inter- 
sected by  canals,  which,  at  the  date  of  their  construction,  were 
the  only  means  of  distributing  power  to  different  mills.  In  the 
course  of  time  these  canals  have  become  lined  with  buildings, 
and  the  land  has  acquired  a  value  of  3,  5,  10  dollars  or  more 
per  square  foot.  A  canal  100  feet  wide  might  carry  10000 
h.p.  on  a  3O-foot  head.  Such  a  canal  would  usually  have 
marginal  reservations  of  1 5  feet  or  thereabouts,  and  the  land 
occupied  by  it  represents  a  value  of  $300  to  $1200  per  linear 
foot.  This  property  is  maintained  as  a  conductor  of  power 
to  perform  a  function  which  might  be  equally  well  fulfilled  by 
copper  wires  of  half  a  square  inch  cross-section  or  by  a  36- 
inch  pipe.  It  appears  probable  that  these  considerations  will, 
before  long,  lead  to  important  modifications  in  existing  ar- 
rangements of  water-powers. 

*Idem. 


CHAPTER    XXII. 
THE   POWER-HOUSE. 

THIS  establishment  contains  the  wheels  and  generators  with 
their  connections  and  appurtenances  for  developing  the  power, 
transforming  it. into  electric  current,  and  controlling  the  delivery 
of  the  latter  to  the  wires.  A  central  establishment  for 
developing  power  and  transmitting  it  to  a  distance  is  wholly  a 
creation  of  the  past  twenty  years.  As  early  as  forty  years  ago 
it  was  found  convenient  in  some  large  manufacturing  establish- 
-ments  to  group  the  turbines  in  one  building  or  one  room, 
called  the  wheel-house  or  wheel-room,  and  couple  them  all  to 
one  shaft  which  supplied  power  to  the  entire  mill  and  often  to 
several  mills.  This  establishment,  through  recent  develop- 
ments in  electricity,  has  grown  into  the  modern  hydraulic 
power-house. 

To  treat  the  subject  of  power-houses  in  detail  would  require 
a  large  folio  volume  of  drawings  and  descriptions,  and  these 
would  become  mainly  obsolete  in  ten  years.  All  that  can  be 
attempted  here  is  a  very  general  view  of  the  subject,  aided  by 
such  sketches  as  can  be  introduced  in  these  pages.  We  will 
consider  the  subject  according  to  the  head  acting  on  the  wheels, 
commencing  with  the  lowest  heads. 

On  such  a  head  as  is  ordinarily  created  by  a  dam  it  is  con- 
venient to  put  the  power-house  in  a  line  with  the  dam  and 
forming  a  part  of  the  same,  being  adapted  to  sustain  the  pres- 
sure of  floods.  The  height  of  floods  should  be  moderated  by 
as  great  a  length  of  overflow  as  possible.  This  is  the  best 
arrangement  when  the  dam  commands  the  entire  fall.  When  it 
is  at  the  head  of  a  rapid  and  it  is  desired  to  make  the  entire  fall 

443 


444  THE  POWER-HOUSE. 

available  by  means  of  a  canal  or  race,  it  will  usually  je  found 
cheaper  to  extend  the  high  level  down  to  the  foot  of  the  rapid 
by  a  canal  than  to  extend  the  low  level  up  to  the  dam  by  a 
race.  This  consideration  would  dictate  placing  the  power- 
house at  the  foot  of  the  rapids,  guarding  against  floods  either 
by  raising  the  river-bank  of  the  canal  above  flood-level  or  by 
a  bulkhead  and  gates  at  the  influx  of  the  canal. 

Fig.  203  shows  a  power-house  on  the  lowest  head  that 
would  be  worth  utilizing,  viz.,  6  feet.  This  design  was  made 
by  the  writer  to  show  the  use  that  could  be  made  of  an 
abandoned  mill  privilege  by  transmitting  the  power  to  other 
mills  owned  by  the  same  corporation  about  a  mile  distant,  in 
a  case  where  the  water  of  the  stream  was  to  be  diverted  for  the 
supply  of  the  Metropolitan  District  of  Massachusetts.  This 
may  be  taken  as  a  type  of  a  low-head  hydraulic  power-house 
lor  electric  transmission.  The  stream  furnishes  water  to  drive 
the  four  wheels  for  three  or  four  months  in  the  year.  At  other 
times  there  will  be  water  for  three,  then  for  two,  then  for  one, 
and  at  times  a  single  wheel  would  have  to  run  at  part  gate. 
The  wheels  are  disconnectible,  and  are  stopped  one  after  another 
according  to  the  stage  of  water,  commencing  with  the  wheel 
most  remote  from  the  dynamo. 

Fig.  205  shows  the  general  situation,  the  canal  and  power- 
house being  indicated  by  dotted  lines.  The  formation  is 
gravel,  with  no  rock  near  the  surface,  and  the  following  mode 
of  construction  is  contemplated  in  the  design.  The  entire  site 
is  excavated  to  a  depth  of  8  feet  below  low  water,  after  exclud- 
ing the  water  of  the  river  by  a  coffer-dam.  A  substantial  bulk- 
head of  masonry  is  laid  across  the  canal,  and  joined  to  the 
bottom  by  a  row  of  sheet-piling  which  extends  well  into  the 
banks  on  each  side.  On  the  down-stream  side  of  the  bulkhead 
a  platform  of  heavy  timbers  covered  with  two  thicknesses  of 
plank  is  laid.  On  this  are  laid  the  walls  of  the  power-house, 
and  the  piers  which  separate  the  wheels.  The  down-stream 
wall  has  four  arched  openings,  through  which  water  escapes  to 
the  river  after  passing  the  wheels.  The  piers  are  built  up  to 


ON  A    LOW  HEAD. 


446 


7 HE   POWER-HOUSE. 


about  the  level  of  low  water  and  sustain  the  floor- timbers  of  the 
flume,  in  fact  the  entire  weight  of  the  flume  and  its  contents. 


Fig.  203«. 


FIG.  203^. 


FIG.  203^. 


Details      of    Gate. 


FIG.  203* 


The  Flume  is  shown  as  one  continuous  basin,  not  separated 
into  compartments,  and  the  bearings  of  the  main  shaft  are 
sustained  by  iron  beams  running  across  from  wall  to  wall. 
This  arrangement  obviates  the  necessity  of  any  water-tight 
connection  between  the  timber  and  masonry,  except  on  the 
up-stream  side..  There  would  be  an  advantage  in  separating 


ON  A    LOW  HEAD. 


447 


448 


THE  POWER-HOUSE. 


the  flume  into  compartments,  one  for  each  wheel,  in  case  of 
repairs  being  required  to  one  wheel  while  others  are  in  motion. 
This  could  very  readily  be  secured  by  carrying  up  a  timber 
bulkhead  over  each  pier,  and  arranging  these  bulkheads  to 
sustain  the  shafting.  We  shall  have  occasion  later  to  discuss 
the  arrangement  in  which  the  stone  piers  are  carried  up  to  the 


FIG.  204. 

dynamo  floor,  and  a  water-tight  connection  is  necessary  between 
the  flume  floor  and  the  masonry  all  around.  The  wheels 
are  14  feet  apart  centre  to  centre.  On  the  1 2-inch  I  beams 
spanning  the  flume  a  framework  of  I  and  channel  bars  is 
erected  to  sustain  the  bridge-trees  and  bearings.  The  crown- 
gears  have  wooden  teeth,  the  jack-gears  are  all  iron;  these 
gears  being  proportioned  to  give  the  required  velocity  to  the 


ON  A    LOW  HEAD. 


449 


450  THE   POWER-HOUSE. 

main  shaft.  A  mortise  spur-gear  on  the  main  shaft  gives 
motion  to  a  countershaft  through  an  iron  pinion,  and  a  pulley 
on  the  countershaft  drives  the  generator  by  means  of  a  belt. 
Undoubtedly  the  latter  might  be  driven  directly  by  toothed 
gears,  but  this  would  involve  a  velocity  rather  in  excess  of  what 
is  considered  safe  for  toothed  gearing.  A  small  pulley  on  the 
dynamo-shaft  drives  the  exciter. 

Horizontal  ledges  run  along  the  side  walls  of  the  power- 
house to -sustain  a  track  on  which  runs  the  travelling  crane,  or 
traveller  as  it  is  called,  which  is  shown  in  the  plan  and  section, 
and  in  detail  at  Figs.  203^"  and  e.  This  is  usually  introduced 
in  power-  houses  for  handling  the  machinery  in  case  of  repairs. 
In  so  small  an  establishment  as  this  it  might  be  omitted  with- 
out serious  disadvantage.  The  use  of  the  traveller  requires  the 
walls  to  be  somewhat  stronger  than  would  otherwise  be  neces- 
sary. 

The  gates  and  mechanism  for  handling  them  are  shown  at 
Figs.  203^,  b,  c,  and  d.  The  disconnecting  couplings  for 
throwing  the  several  wheels  in  and  out  of  connection  are  sup- 
posed to  be  of  the  form  shown  at  Fig.  164.  With  these 
arrangements  it  will  be  perceived  that  no  wheel  can  run  while 
a  wheel  to  the  right  of  it  is  stopped.  If  it  were  desired  to 
arrange  the  mechanism  so  that  any  wheel  could  be  stopped 
with  the  others  running,  the  simplest  way  is  to  introduce 
mechanism  for  lowering  the  crown-gear  and  drawing  it  out  of 
connection  with  the  jack.  (See  Fig.  163.) 

This  design  shows  in  a  strong  light  the  disadvantage  of  a 
low  head,  in  respect  of  the  cumbrous  character  of  the  mechanism 
required  to  raise  the  velocity  to  the  rate  called  for  by  electricity. 
On  a  sufficiently  high  head  the  dynamo  can  be  coupled  directly 
to  the  horizontal  shaft  and  save  the  expense  and  loss  of  power 
incident  to  intermediate  connections. 

The  Lachine  Rapids  Power-house.* — Fig.  206  shows  in 
plan  the  power-house  and  appurtenances  at  the  Lachine 

*  This  description  is  gathered  mainly  from  an  article  in  Engineering 
News,  February  18,  1897. 


AT    THE  LA  CHINE  RAPIDS.  45  I 


452  THE  POWER-HOUSE. 

Rapids  on  the  St.  Lawrence  River  some  6  miles  above  Mon- 
treal. This  is  one  of  the  numerous  rapids  which  occur  on  the 
St.  Lawrence  between  Lake  Ontario  and  tide-water.  They 
occupy  some  5  miles  of  the  river-channel,  with  a  total  fall  of 
about  30  feet.  A  dam  across  the  river  here  would  not  be 
permissible  even  were  such  a  work  practicable.  The  only 
mode  of  making  the  fall  available  was  to  construct  a  spur-dam, 
which  we  call  the  main  dani,  at  right  angles  to  tne  shore, 
extending  into  the  stream  a  sufficient  distance,  and  from  that 
point  to  extend  a  wing-dam  up  the  stream  to  a  distance  suffi- 
cient to  raise  the  required  head.  Fig.  2O//  shows  the  general 
situation  and  surroundings.  Fig.  207^-  shows  the  main  dam, 
wing-dam,  and  booms  fc^r. protecting  the  work  from  ice.  Fig. 
207 k  is  a  longitudinal  section  showing  the  wing-dam  in  eleva- 
tion. The  wing-dam  extends  some  3700  feet  above  the  main 
dam  and  I2OO  below.  This  latter  portion  adds  to  the  fall  by 
excluding  the  river  from  the  tail-race.  Otherwise  stated,  the 
improvement  consists  in  partitioning  off  a  part  of  the  river- 
channel  by  a  wing-dam  parallel  to  the  shore,  and  constructing 
a  dam  across  this  new  channel,  to  utilize  the  fall  therein.  The 
wing-dam  reaches  nearly  to  the  head  of  the  rapids,  the  main 
part  of  which  is  below  the  works.  The  total  fall  utilized  is 
about  1 2  feet. 

From  the  inception  of  this  enterprise  it  was  apprehended 
that  ice  would  be  a  serious  obstacle  to  the  operation  of  the 
works,  and  the  construction  was  largely  modified  by  this 
expectation.  At  Fig.  207^-  two  long  booms  are  shown,  reach- 
ing from  the  shore  to  the  wing-dam  and  sustained  by  cribs 
filled  with  stone.  Between  these  booms  the  wing-dam  is  over- 
flowable,  and  of  the  construction  shown  at  Fig.  207^.  The 
construction  of  the  booms  is  shown  at  Figs.  207^  and  e.  They 
have  mass  and  stability  enough  to  sustain  any  number  of  men 
necessary  to  keep  them  free  of  ice.  The  upper  boom  is  sup- 
posed to  prevent  the  entrance  of  ice  into  the  water-power 
channel.  The  lower  one  is  intended  to  exclude  any  ice  which 
passes  the  upper  boom  or  forms  in  the  channel,  and  throw  the 


AT   THE  LA  CHINE   XAPIDS. 


453 


same  over  the  wing-dam.      In  addition  there  is  a  system  of 
booms  attached  to  the  main  dam  for  sluicing  ice  through  waste- 


FIG. 


BKHRW 


FIG.  2073.  FIG.  207*:. 

ways  in  the  latter.     The  construction  of  these  wastevvays  is 
shown  at  Figs.  2070  and  b. 


454 


THE  POWER-HOUSE. 


AT    THE   LA  CHINE    RAPIDS.  455 

The  ice  to  be  guarded  against  is  of  two  kinds :  anchor-ice, 
or  frazil-ice  as  it  is  here  called,  which  forms  on  the  surface  of 
rapidly  running  waters  and  ceases  to  run  when  the  stream 
freezes  over,  and  the  heavy  ice  brought  down  at  the  annual 
breaking  up.  The  St.  Lawrence  flowing  northward,  and 
commencing  to  break  up  at  the  head,  the  ice-jams  are  very 
formidable,  and  it  remains  to  be  seen  how  these  works  will 
stand  against  them. 

The  main  dam  is  merely  a  series  of  flumes,  power-houses, 
and  wasteways.  A  general  idea  of  it  is  given  in  Fig.  2O?g. 
It  consists  of  a  row  of  piers  extending  entirely  across  the 
channel  and  sustaining  the  machinery  and  buildings.  Except 
at  the  power-houses  these  piers  are  48  feet  long  up  and  down 
stream,  and  about  21  feet  apart  centre  to  centre.  Up  to  the 
floors  of  the  flumes  these  piers  are  of  concrete  5  feet  thick ; 
above  this  level  they  are  of  cut-stone  masonry  4  feet  thick. 
The  piers  rise  about  6  feet  above  ordinary  water-level,  which 
is  thought  to  be  sufficient,  as  the  fluctuations  of  the  St.  Law- 
rence are  not  great.  A  rise  in  the  river  here  does  not  imply 
a  corresponding  rise  immediately  above  the  main  dam.  A  rise 
of  5  feet  at  the  latter  point  would  imply  some  140  ooo  cubic 
feet  per  second  going  over  the  wing-dam,  which  would  greatly 
lower  the  level  in  the  channel. 

The  floors  of  the  flumes  are  supported  by  timbers  1 2  inches 
wide,  15  inches  deep,  imbedded  at  their  ends  in  the  concrete 
masonry,  and  these  are  also  supported  by  cast-iron  columns. 
Near  the  upper  end  of  the  pier  is  a  check  12  inches  wide, 
8  inches  deep  for  the  gate,  and  near  the  lower  end  is  a  similar 
check  for  a  barrier  of  stop-logs.  This  latter  feature  was,  it  is 
presumed,  introduced  on  the  ground  of  economy.  The  sub- 
stantial construction  would  have  consisted  in  throwing  an  arch 
over  the  lower  end  of  the  wheel-pit,  with  its  soffit  at  low-water 
level,  and  resting  a  heavy  wall  thereon  united  with  the  piers. 
The  stop-logs  are  strengthened  by  the  inclined  iron  tie-rods 
appearing  in  Fig.  207,  which  are  attached  to  a  channel-bar 
placed  vertically  on  the  down-stream  side  of  the  stop- logs,  and 


456  THE  POWER-HOUSE. 

at  their  up-stream  ends  to  a  long  iron  plate  bolted  to  a  number 
of  the  floor-beams.  The  gates  are  only  inserted  in  emergen- 
cies. They  are  handled  by  the  travelling  crane  and  are 
ordinarily  kept  stored  under  water.  The  piers  support  steel- 
frame  sheds  erected  over  the  wheels  and  shafting,  and  substan- 
tial buildings  of  brickwork  and  skeleton  steel  cover  the  electric 
machinery,  constituting  the  power-houses  proper,  the  whole 
forming  a  continuous  building  nearly  I OOO  feet  in  length,  through 
which  a  25-ton  hand-power  travelling  crane  runs  from  end  to 
end.  Two  of  the  wheel-pit  spaces  are  occupied  by  wasteways 
for  sluicing  off  the  ice  diverted  into  them  by  the  booms.  The 
heavy  rings  anchored  in  the  walls,  as  shown  at  Figs.  207  £  and 
<?,  are  for  the  attachment  of  the  booms.  When  racks  are 
exposed  unprotected  to  heavy  flake  and  anchor  ice,  the  latter 
is  liable  to  pack  solidly  against  them  from  top  to  bottom. 
The  water  in  the  flumes  escapes  through  the  wheels,  leaving 
the  pressure  of  the  entire  head  acting  on  the  racks,  which  are 
then  very  liable  to  break  down. 

Wheels. — Each  flume  contains  two  special  54-inch  Victor 
turbines,  a  total  of  72,  which  are  connected  in  sets  of  6  turbines 
to  each  of  12  generators,  4  in  each  power-house.  These  wheels 
are  set  vertically  on  3 -inch  plank  flooring  and  will  develop 
200  h.p.  each  under  a  head  of  n  feet,  a  total  of  14400  h.p. 
Under  this  head  they  run  at  64  revolutions  per  minute,  dis- 
charging 200  cubic  feet  of  water  each  per  second,  being  a  total 
discharge  of  14400  cubic  feet  per  second.  This  is  but  an  in- 
significant fraction  of  the  total  flow  of  the  stream,  which  carries 
here  not  less  than  a  quarter  of  a  million  cubic  feet  per  second, 
including  the  channel  to  the  northward  of  the  island  of 
Montreal. 

Each  set  of  6  wheels  is  connected  by  bevel-core  gears  to  a 
common  jack-shaft  which  transmits  their  power,  at  a  speed  of 
175  revolutions  per  minute,  to  a  3 -phase  generator  of  750 
K.W.  guaranteed  to  stand  25  per  cent  overload.  The  speed 
is  regulated  by  a  governor  guaranteed  to  control  it  within  2  per 
cent  from  O  to  full  load.  The  gears  and  shafting  are  sustained 


MECHANICSVILLE   OAT    THE  HUDSON.  457 

by  bridge-trees  resting  on  1 2-inch  I  beams  which  extend  from 
pier  to  pier. 

Mechanicsville  on  the  Hudson. — Figs.  208  and  209  relate 
to  the  power-house*  at  Mechanicsville  on  the  Hudson  River 
about  1 8  miles  above  Albany,  which  city,  together  with  Troy, 
some  1 1  miles  distant,  has  large  use  for  power.  At  Schenec- 
tady,  17  miles  away,  are  the  great  works  of  the  General  Electric 
Company,  covering  some  130  acres  of  ground,  and  it  was  chiefly 
with  a  view  to  supplying  these  works  that  this  development 
was  undertaken. 

The  river  at  this  point  is  about  1200  feet  wide.  It  is 
separated  by  Bluff  Island  into  two  channels,  the  westerly  about 
400,  the  easterly  some  800  feet  in  width.  The  ordinary 
summer  flow  of  the  Hudson  at  this  point  may  be  placed  at 
4000  or  5000  cubic  feet  per  second,  though  often  falling  much 
below  the  lower  figure.  The  available  fall  is  18  feet.  The 
westerly  channel  is  occupied  by  the  power-house,  supplemented 
by  a  bulkhead  rising  above  high  water,  and  is  entirely  closed 
to  the  passage  of  floods.  The  easterly  channel  is  occupied  by 
the  overflow-dam  already  noticed,  page  ill.  A  floating 
boom,  anchored  to  timber  cribs  filled  with  stone,  extends 
obliquely  across  the  westerly  channel  for  the  exclusion  of  drift. 
The  lower  part  of  the  power-house  is  of  concrete  resting  on 
rock.  The  floor  is  formed  by  arches  springing  from  steel  box 
girders  which  are  supported  by  steel  I-beam  columns.  A  con- 
crete head -wall  6  feet  thick  divides  the  floor  into  two  parts. 
The  up-stream  portion  is  the  flume,  containing  the  wheels  and 
draft-tubes.  The  down-stream  part  is  the  generator-room, 
which  the  horizontal  shafts  enter  through  stuffing-boxes  in 
plates  built  into  the  concrete  wall.  Along  the  up-stream  face 
of  the  power-house  runs  a  rack  formed  of  flat  steel  rods,  sus- 
tained by  a  frame  of  steel  beams  and  pillars,  the  whole  sur- 
mounted by  a  bridge  for  the  convenience  of  workmen  in 
cleaning  the  racks.  There  are  ten  pairs  of  42-inch  horizontal 

*  The  drawings    and  description    of  this    plant    are  from    Engineering 
News,  vol.  XL.  p.  130,  and  EngineeringRecord,  vol.  xxxvm.  p.  299. 


458 


POWER-HOUSE. 


MECHANICSVILLE    ON    THE  HUDSON. 


459 


Victor  turbines,  two  pairs  on  each  shaft.  On  the  obtainable 
head  of  18  feet  these  run  at  114  turns  per  minute,  each  wheel 
being  rated  at  250  h.p.  and  each  set  of  four  driving  a  750- 


K.W.  generator.  Two  additional  sets  of  wheels  are  contem- 
plated for  the  future,  making  -a.  total  development  of  7000  h.p. 
A  development  of  7000  or  even  5000  h.p.  would  in  the  normal 


460  THE  POWER-HOUSE. 

state  of  the  river  be  subject  to  serious  interruptions.  Data 
obtained  by  Mr.  Geo.  W.  Rafter  in  the  course  of  examinations 
relative  to  the  system  of  reservoirs  proposed  by  the  State  of 
New  York,  showed  that  the  flow  of  the  Hudson  at  Mechanics- 
ville  was  under  1500  cubic  feet  per  second  (less  than  3000 
h.p.)  for  124  days  in  the  eight  years  terminating  with  1895. 
On  this  account  the  design  of  the  power-house  contemplated 
the  possibility  of  supplementary  steam-power  to  meet  the 
variations  of  the  stream.  To  this  end  a  disconnecting  coupling 
is  introduced  on  the  dynamo-shaft,  and  the  other  end  of  the 
shaft  is  formed  with  a  view  to  connection  with  a  vertical  steam- 
engine.  It  is  probable,  however,  that  the  progress  thus  far 
made  in  the  execution  of  the  State's  system  of  reservoirs  will 
obviate  any  necessity  for  the  introduction  of  steam.  Each  pair 
of  wheels  discharges  through  a  draft-tube,  which  has,  as  will 
be  noticed,  a  flaring  shape,  being  largest  at  the  bottom.  The 
effect  of  this  disposition  is  analogous  to  that  of  the  diffuser  of 
the  Boyden  turbine  (see  page  309).  The  exciter- wheels,  which 
appear  on  the  plan,  are  1 8-inch  cylinder-gate  Victor  turbines 
running  259  turns  per  minute. 

The  regulators  occupy  the  platforms  over  the  wheel-shafts  in 
the  generator-room.  These  are  of  the  Geisler  electro-mechani- 
cal type  and  are  said  to  be  so  sensitive  that  the  gates  can  be 
entirely  opened  or  closed  in  6  seconds.  The  exciter-wheel 
gates  are  controlled  by  "snow"  governors  provided  with 
adjustable  stops  which  limit  the  hoisting  action  as  soon  as  the 
gate  is  fully  open. 

The  generators  occupy  a  well-lighted  room  255  feet  long, 
34  feet  wide,  and  30  feet  5  inches  from  floor  to  roof- truss.  The 
entire  area  of  the  room  is  commanded  by  a  2O-ton  travelling 
crane.  As  already  stated,  the  ultimate  generator  capacity  of 
the  station  is  7000  h.p.  in  7  generators  of  750  K.W..  capacity, 
though  only  5  generators  had  been  installed  at  the  date  of  this 
information  (1898).  These  are  uni-tooth,  3-phase.  4O-pole, 
75O-K.W.,  1 14-revolution  alternating  machines,  having  revolv- 
ing fields  and  stationary  armatures.  They  are  wound  to  deliver 


SAULT  STE.    MARIE.  461 

to  the  transmission-lines  36  amperes  at  a  periodicity  of  38  cycles 
and  a  pressure  of  12  ooo  volts,  and  are  arranged  for  operation 
in  parallel  at  constant  voltage.  By  using  the  revolving-field 
type  of  generator  it  is  possible  to  secure  this  high  voltage 
directly  from  the  machine  without  the  use  of  transformers. 
As  the  current  is  to  drive  synchronous  and  induction  motors, 
to  operate  lights,  and  to  be  converted  into  direct  current  through 
rotary  converters,  a  frequency  of  about  40.  cycles  was  selected 
as  most  suitable. 

The  exciters  for  magnetizing  the  fields  of  the  generators 
are  placed  one  on  each  side  of  the  stairway  leading  to  the 
switchboard  gallery.  They  are  6-pole,  IOO-K.W.,  125-volt 
standard  General  Electric  machines  with  ribbed  field-frame 
and  iron-clad  armatures. 

Fig.  210  with  subsketches  2ioaand  b  shows  a  general  idea 
of  the  proposed  power-house  of  the  Michigan  Lake  Superior 
Power  Company  on  the  Canadian  side  of  Sault  Ste.  Marie. 
These  are  from  blue-prints  kindly  furnished  in  advance  of  the 
entire  maturity  of  the  plans  by  Mr.  H.  von  Schon,  the  engineer 
of  this  work.  Between  Lakes  .Superior  and  Huron  there  is  a 
fall  of  19  to  20  feet,  which  is  substantially  all  concentrated  at 
a  single  rapid.  By  means  of  a  canal  something  over  2  miles 
long,  this  fall  is  made  available  at  the  power-house.  This  is 
in  one  sense  the  largest  water-power  development  yet  under- 
taken, not  in  the  sense  of  developing  the  largest  amount  of 
power,  but  in  the  sense  of  using  the  largest  quantity  of  water, 
viz.,  30000  cubic  feet  per  second.  The  canal  is  constructed 
with  a  view  to  the  attainment  of  a  high  velocity  without  undue 
loss  of  head.  It  is  partly  in  rock  formation,  partly  in  earth. 
The  rock  is  to  be  cut  vertically  with  channelling-machines ;  the 
bottom  is  to  be  made  smooth  with  hydraulic  cement  mortar. 
The  earth  part  is  to  have  a  smooth  and  even  lining  of  timber 
and  plank.  By  these  means  it  is  expected  to  secure  a  velocity 
of  7  feet  per  second  and  a  head  of  16  feet  at  the  power-house. 
Assuming  a  loss  of  i  foot  in  penstocks  and  wheel-pits,  and  an 
efficiency  of  80  per  cent  in  the  wheels,  this  would  realize  some 


462 


THE   POWER-HOUSE. 


41  ooo  h.p.  The  flow  of  Sault  Ste.  Marie  ranges  from  6ooco 
to  i  oo  ooo  cubic  feet  per  second  according  to  the  stand  of 
Lake  Superior. 

Fig.  210  is  a  general  section  of  the  power-house,  which  has 
a  length  of  about  a  quarter  of  a  mile.      Fig.  2100  shows,  on  a 


FIG.  210. 

small  scale,  the  general  arrangement  of  the  wheel-pits,  eighty 
in  number,  each  containing  two  wheels  or  two  pairs  of  wheels. 
The  upper  part  of  the  building  is  reserved  for  industries 
dependent  on  the  water-power,  but  the  greater  part  of  the 
latter  will  be  applied  to  the  production  of  electric  current. 
This  locality  being  remote  from  any  large  centre  of  industry,  it 


SAULT  STE,    MARIE. 


463 


is   not  known   to  what 'purpose   the   electric    current  will   be 
applied. 

The  building  differs  from  the  types  hitherto  considered,  in 
not  being  provided  with  a  travelling  crane.  The  unusual  width 
of  the  building,  and  the  intermediate  floor,  forbid  this  appurte- 


o 

o 

o 

o 

o 

0 

7 

o 

o 

o 

0 

0 

o 

0 

5 

o 

. 

FIG.  2100. 


FIG.  2io3. 

nance.  Instead  of  the  crane,  light  cars  running  on  service- 
tracks  are  to  be  used  for  the  moving  of  machinery.  Along 
the  front  of  the  building  arrangements  are  made  for  the  attach- 
ment and  movement  of  a  small  boom-derrick  to  handle  the 
penstock-gates.  Fig.  210^  shows  one  of  the  flumes  or  pen- 
stocks in  plan.  These  are  constructed  of  steel  plates  supported 
by  a  framework  of  steel  beams.  Nothing  of  the  wheels  appears 
except  the  draft-tubes.  It  is  understood  that  horizontal  wheels 
are  to  be  used,  the  shafts  passing  through  stuffing-boxes  in  the 
flumes  and  extending  to  the  dynamo  floor. 


464 


THE  POWER-HOUSE. 


For  a  Power-house  Supplied  by  a  Pipe  under  a  head  of 
200  feet  or  less  Fig.  2 1 1  indicates  a  suitable  arrangement. 
It  is  suposed  to  be  located  near  the  watercourse  which  receives 


FIG.  211. 

the  discharge,  and  the  sketch  assumes  a  rock  formation.  A 
tail-race  is  cut  leading  into  the  watercourse.  In  a  soft  forma- 
tion this  would  be  provided  with  side  walls  and  a  plank  or 
concrete  bottom.  An  arch  is  thrown  over  this  channel  and 
levelled  up  with  concrete,  which  extends  the  whole  width  of 
the  building,  forming  the  basement  floor.  The  basement  con- 
tains the  supply-pipe  and  wheels,  the  former  running  length- 
wise of  the  building  and  sending  off  branches  at  suitable 
intervals  to  drive  the  wheels.  The  sketch  assumes  a  head  of 
200  feet  and  a  velocity  of  some  7  feet  per  second  in  the  supply- 


SUPPLIED   BY  A    PIPE.  465 

pipe.  With  such  great  heads  it  is  not  customary  to  count  the 
loss  of  head  so  closely  as  is  proper  with  ordinary  heads.  The 
wheel  is  supposed  to  draw  about  50  cubic  feet  per  second, 
giving  something  over  800  h.p.  A  wheel  of  ordinary  propor- 
tions under  this  head  would  have  too  rapid  a  velocity,  as  it 
would  not  have  a  diameter  greater  than  1 5  inches  and  would 
revolve  as  much  as  1000  times  a  minute.  To  limit  the  velocity 
to  500  turns  a  minute,  its  diameter  must  be  as  much  as  30 
inches  and  the  discharge  must  be  restricted  by  limiting  the 
height  of  the  orifices.  The  wheels  discharge  through  draft- 
tubes  passing  through  the  arch  and  dipping  into  the  tail-race. 
The  generator  floor  is  sustained  by  steel  beams  extending  from 
wall  to  wall,  and  may  consist  of  arches  resting  on  the  lower 
flange  of  the  beam  or  of  thick  planking.  Planking  may  be 
laid  on  steel  I  beams  by  attaching  a  timber  to  the  latter  con- 
fined by  bolts  through  the  web.  The  generator  is  directly 
coupled  to  the  shaft.  It  is  represented  with  a  revolving  arma- 
ture and  stationary  field,  though  the  reverse  arrangement  is 
more  common.  The  weight  of  the  revolving  part  comes  upon 
the  shaft  and  is  borne  by  the  thrust-bearing,  Fig.  212.  The 


FIG.  212. 


weight  of  the  wheel  and  other  revolving  parts  may  be  thrown 
upon  the  same  bearing  if  desired,  and  this  is  generally  the  more 
judicious  arrangement,  as  it  admits  of  more  efficient  lubrication 
than  the  ordinary  bearing  at  the  bottom  of  the  shaft. 

For  heads  exceeding  200  feet,  and  even  for  heads  exceed- 


466 


THE  POWER-HOUSE. 


ing   100  where  the  velocity  of  the   generator  is   limited,  the 
disposition  of  Fig.  213  may  be  adopted.     The  general  arrange- 


FIG.  213. 

ment  of  the  power-house  is  the  same  as  the  preceding,  but  we 
adopt  a  different  form  of  wheel,  viz.,  the  hurdy-gurdy  wheel 
driven  -by  a  jet  of  water  acting  on  cup-shaped  vanes  (see  page 
300).  The  peculiar  adaptability  of  this  wheel  consists  in  the 
fact  that  a  low  velocity  of  rotation  can  be  imparted  to  the  shaft 
under  the  highest  head  by  giving  the  wheel  a  suitable  diameter. 
The  head,  in  this  case,  is  assumed  to  be  1000  feet,  implying  a 
velocity  of  254  feet  per  second.  The  diameter  of  the  wheel  is 
12  feet  measured  to  the  centre  of  the  vanes,  and,  as  it  gives  its 
best  effect  with  a  velocity  of  vane  equal  to  half  that  of  jet,  the 
speed  will  be  127  X  60/12  X  n  =  200  per  minute.  A  3-inch 
stream  would  carry  12.4  cubic  feet  of  water  per  second  and 
would  furnish  over  1000  h.p.  As  in  the  former  case,  the  tail- 


SUPPLIED  BY  A    PIPE. 


467 


468  THE  POWER-HOUSE. 

race  is  covered  by  an  arch,  but  this  is  interrupted  at  each  of 
the  wheels,  leaving  an  open  space  for  the  insertion  of  the  wheel, 
the  case  of  which  rests  on  the  masonry  by  means  of  a  flange. 
This  arrangement  also  leaves  an  open  space  for  the  nozzle, 
which,  together  with  the  recess  in  which  the  supply-pipe  lies, 
is  covered  with  planking.  The  overhead  crane  cannot  be  dis- 
pensed with  in  this  power-house,  as  accidents  are  more  liable 
to  occur  under  such  high  heads  than  under  low  heads. 
Especially  if  the  water  carries  gravel  or  sand,  the  buckets  of 
the  wheel  are  liable  to  very  rapid  wear,  and  the  wheel  to 
require  frequent  repairs  and  renewals. 

The  regulation  of  wheels  supplied  through  long  pipes  is 
subject  to  peculiar  difficulties,  as  already  pointed  out  (see  page 
332),  owing  to  the  enormous  weight  of  the  column  of  water 
which  has  to  be  checked  when  the  discharge  of  the  wheels  is 
diminished.  Where  great  elevations  occur  in  the  immediate 
vicinity  of  the  power-house,  the  following  method  is  prac- 
ticable and  effectual,  though  expensive:  Connect  the  supply- 
pipe  at  the  power-house  with  a  pipe  of  equal  size  leading  to  an 
elevation  equal  to  that  of  the  source  of  supply  diminished  by 
the  frictional  head  in  the  pipe,  these  communicating  with  a 
small  reservoir  so  formed  that  the  water  may  rise  to  the  level 
of  the  source  and  a  little  higher  without  overflowing.  In  this 
arrangement  the  sudden  diminution  of  the  discharge  of  the 
wheels  does  not  immediately  diminish  the  velocity  in  the  pipe. 
The  water  continues  to  flow  for  a  few  seconds  with  sensibly 
unabated  velocity,  but  discharges  into  the  reservoir  instead  of 
through  the  wheels.  Of  course  the  pipe  leading  to  the  reser- 
voir may  be  made  smaller  than  the  supply-pipe  without,  being 
valueless,  but  the  diminution  of  its  size  will  be  accompanied  by 
a  more  than  proportional  diminution  of  its  efficiency. 

An  Air-chamber  in  lieu  of  the  preceding  arrangement  for 
moderating  the  fluctuations  of  pressure  is  a  very  natural  sug- 
gestion. Some  advantage  may  be  derived  from  this  attach- 
ment, but  it  is  liable  to  more  serious  objections  than  appear  at 
first  sight.  It  must  have  great  size  in  order  to  be  of  any  value, 


AIR-CHAMBER   ON  PENSTOCK.  469 

and  with  any  rational  size  the  variations  of  pressure  are  greater 
than  desirable.  To  form  some  idea  of  the  size,  suppose  a  pipe 
I  mile  in  length  with  a  head  of  2OO  feet  on  the  wheels.  Sup- 
pose a  velocity  in  the  pipe  of  6  feet  per  second  and  impose  the 
condition  that  it  can  suddenly  be  reduced  to  3  feet  without 
changing  the  pressure  mpre  than  20  per  cent.  Consider  only 
a  portion  of  the  pipe  I  square  foot  in  cross-section.  A  velocity 
of  6  feet  per  second  implies  an  amount  of  energy  equal  to 
36/2^-  X  5280  =  9/16  X  5280  cubic  feet  of  water  raised  i  foot. 
One  of  3  feet  represents  9/64  X  5280.  A  change  from  6  to  3 
implies  the  absorption  .of  energy  equal  to  27/64  X  5280  = 
2227.5  cubic  feet  water  raised  I  foot,  or,  what  is  the  same  thing, 
1 1 1  cubic  feet  raised  2O  feet.  The  increase  of  head  is  O  at  the 
instant  of  shutting  off,  and  is  limited  to  40  feet  at  the  instant 
the  velocity  reaches  3  feet  in  the  supply-pipe,  so  that  the 
average  head  which  opposes  the  momentum  of  the  water  is  20 
feet,  and  under  this  excess  of  head  1 1 1  cubic  feet  of  water  will 
enter  the  chamber  before  the  movement  is  checked  to  the 
assumed  extent.  Let  v  be  the  volume  of  air  at  the  normal 
pressure.  We  have  the  relation  2OOZ-*  =  240 (v  —  in), 
whence  v  =  666.  That  is  to  say:  to  meet  the  above  condi- 
tions, the  chamber  should  have  a  capacity  of  666  cubic  feet  for 
each  square  foot  of  cross-section  of  the  supply-pipe  and  each 
mile  of  its  length,  requiring  for  a  pipe  5  miles  long  and  6  feet 
diameter  a  capacity  of  94  1 56  cubic  feet,  being  equivalent  to 
3330  linear  feet  of  6-foot  pipe.  The  compression  of  the  air  and 

consequent  slowing  up  of  the  velocity  occupies  about  —^  —  1 8 

seconds.  Then  the  air  expands  and  the  pressure  diminishes 
till  it  reaches  near  40  feet  head  below  the  normal,  and  a  series 
of  long  oscillations  occur.  To  obviate  this  result  it  has  been 
suggested  that  the  communication  between  the  pipe  and  air- 
chamber  should  be  nearly,  but  not  quite,  closed  by  a  flap-valve 

*  When  a  given  quantity  of  air  changes  its  pressure  at  constant  tem- 
perature the  product  of  the  volume  by  the  pressure  remains  constart. 
See  p.  413- 


47°  THE   POWER-HOUSE. 

opening  toward  the  chamber,  allowing  the  water  to  flow  freely 
into  the  latter,  but  making  its  return  very  slow. 

The  most  perfect  remedy  for  the  difficulties  of  regulation  in 
long  pipe  systems  is  one  which  dispenses  with  any  necessity 
for  regulation,  viz.,  a  sufficient  storage-battery,  which  absorbs 
the  surplus  power  when  in  excess  of  requirements  and  gives 
out  power  when  the  demand  exceeds  the  supply,  thus  allowing 
the  wheels  to  run  with  absolutely  uniform  discharge. 

Hydraulic  Compressed-air  Power-house. — The  method  of 
compressing  air  by  the  direct  action  of  water  already  summarily 
described  (page  426)  has  been  applied  at  Magog,  P.  Q.,  and  is 
now  in  course  of  installation  at  Taftville,  Conn.  (1900).  It  is 
therefore  entitled  to  a  place  in  a  description  of  methods  of 
developing  water-power.  Being,  moreover,  adapted  for  the 
generation  of  power  on  a  large  scale,  it  may  properly  be  con- 
sidered under  the  head  of  Power-houses. 

Figs.  215  and  2150  show  the  application  of  the  method  as 
proposed  by  the  writer.  Fig.  216  is  a  section  of  the  apparatus 
used  at  Magog,  P.  Q.  The  water  is  here  supplied  through  a 
penstock  and  enters  a  circular  plate-iron  tank,  which  we  may, 
by  analogy,  call  the  flume.  From  this  flume  a  circular  pipe 
3  feet  in  diameter  descends  vertically  into  a  pit,  to  a  depth  im- 
plying a  pressure  of  52  pounds  per  square  inch.  This  pipe 
discharges  into  another  tank,  larger  than  the  first,  covered  on 
top  and  open  at  the  bottom,  which  is  fixed  some  2  feet  above 
the  floor  of  the  pit.  This  we  call  the  air-chamber.  It  has  a 
diaphragm,  not  shown,  the  purpose  of  which  is  to  detain  the 
water  in  the  chamber  and  facilitate  the  elimination  of  the  air. 
In  the  flume  there  is  a  separate  pipe  some  10  feet  long,  with  a 
wide  flaring  mouth  at  top,  telescoping  into  the  descending  pipe, 
and  adjustable  vertically  by  a  screw  and  hand-wheel  seen 
above  the  flume.  Above  the  mouth  of  the  telescoping  pipe  is 
a  circular  frame  bearing  a  system  of  short  vertical  2-inch  tubes, 
the  upper  ends  of  which  are  open  and  the  lower  ends  dip  into 
the  water.  The  part  of  the  tube  immersed  in  water  is  provided 
with  a  number  of  £-inch  orifices,  in  which  small  pipes  6  or  8 


HYDRAULIC   COMPRESSION  OF  AIR. 


4/1 


inches  long  are  inserted  all  horizontal  and  pointing  inward, 
i.e.,  toward  the  centre  of  the  3-foot  pipe.  The  water  passing 
the  system  of  pipes  in  rapid  movement,  the  pressure  at  the  free 


FIG.  215. 


FIG.  2150. 

ends  of  the  small  pipes  is  less  than  that  of  the  atmosphere,  and 
air  in  small  bubbles  enters  the  water  and  is  carried  downward. 
The  pit  toward  the  bottom  is  enlarged  for  the  accommodation 
of  the  air-chamber,  and  from  the  summit  of  the  latter  a  7-inch 


472 


THE  POWER-HOUSE. 


HYDRAULIC   COMPRESSION   OF  AIR.  4/3 

pipe  leads  upward  and,  after  passing  the  level  of  the  tail-race, 
turns  horizontally  toward  the  mill  requiring  power. 

Operation. — The  water  is  set  in  motion  by  lowering  the 
telescopic  pipe,  the  position  of  the  mouthpiece  determining  the 
quantity  of  water  flowing  through  the  system.  Air  enters 
through  the  small  pipes  and  is  carried  downward  into  the  air- 
chamber.  The  water,  supposed  to  be  freed  from  air,  passes 
under  the  rim  of  the  air-chamber,  rises  through  the  pit,  and 
flows  away  through  the  tail-race.  The  air  accumulates  in  the 
chamber  under  a  pressure  represented  (when  the  water  is  not 
moving)  by  the  depth  of  the  surface  in  the  air-chamber  below 
the  surface  in  the  tail-race. 

Figs.  215  and  2i$a  show  the  system  already  partly 
described  (page  426).  We  may  add  that  these  figures  contem- 
plate a  telescoping  pipe  entering  the  descending  shaft,  carrying 
a  hopper-shaped  mouthpiece,  which  we  will  call  the  hopper-, 
and  adjustable  vertically  by  mechanism  not  shown.  The 
hopper  is  guided  in  its  vertical  movement  by  four  piers  shown 
in  Fig.  215^.  These  form  four  channels  of  approach  through 
which  four  currents  of  water  enter  the  hopper  and  in  meeting 
cause  the  necessary  commotion.  It  was  clearly  shown  by  the 
writer's  experiments  at  Minneapolis,  in  1880,  that  throwing 
the  water  into  commotion  is  a  perfectly  effective  mode  of  im- 
pregnating it  with  air.  Any  arrangement  of  pipes  for  this  pur- 
pose appears  to  the  writer  entirely  superfluous,  as  well  as  very 
objectionable.  The  pipes  could  not  fail  at  times  to  become 
clogged  with  floating  debris  to  the  extent  of  wholly  arresting 
the  flow  of  water.  In  the  arrangement  of  Fig.  215,  trash  of 
every  kind,  blocks  of  ice,  and  even  logs  could  go  through  the 
system  without  embarrassment  or  interruption,  not  even  a  rack 
being  required.  In  this  disposition  the  position  of  the  hopper 
determines  the  quantity  of  water  drawn.  The  quantity  of  air 
regulates  itself  and  is  neither  more  nor  less  than  the  given 
quantity  of  water  can  carry.  If  tfre  descending  column  is  so 
loaded  with  air  that  it  does  not  preponderate  sufficiently  over 
the  ascending  column,  the  water  in  the  former  will  rise,  the 


474  THE  POWER-HOUSE. 

commotion  will  diminish,  and  less  air  will  enter.  In  the  con- 
trary case  the  water  falls,  commotion  increases,  and  more  air 
is  taken  in. 

It  may  be  useful  to  attempt  an  approximate  estimate  of  the 
efficiency  of  this  method  upon  admitted  principles  of  hydraulics. 
Instead  of  attempting  a  general  discussion  of  the  matter  we 
will  assume  specific  data  as  follows:  Circular  channels  lined 
with  brickwork  with  uniform  diameter  of  10  feet;  a  velocity  of 
8  feet  per  second;  a  head  of  24  feet;  a  pressure  of  100  pounds 
net,  i.e.,  100  pounds  above  the  atmosphere.  We  assume  the 
ascending  shaft  to  widen  so  as  to  reduce  the  velocity  of  efflux 
to  4  feet. 

1.  Fall  at  influx,  or  that  required  to  impregnate  the  water 
Avith  air.      The  arrangement  of  Fig.  215  is  more  efficient  in 
this  regard  than  that  used  at  Minneapolis,  in  which  this  loss  did 
not  exceed 1 .00 

2.  The  head  due  the  velocity  of  8  feet  would  be  i.oo 
foot,  but  we  need  only  consider  the  head  due  the  velocity 

of  efflux,  which  is 0 0.25 

3.  Loss  due  to  friction  in  the  channels  =  h.     We  will 
use  the  formula  v  =  c  Vrs.     We  will  call  the  total  length 
of  the  channel  650  feet,  so  that  s  =  7/7650.     We  have 
r  =  2.50.      Experiments  on' the  Sudbury  River  conduit 
pertaining  to  the  Boston  Water-works  show  that  for  a 
surface  of  brickwork  carefully  laid  c  may  be  taken  =i  140. 

We    have    therefore  v^  —  64  =  19600  X  2.5  X  ^ — , 

050 

64  X  650 

Avhence  h  =  —  —  — 0.85 

19  600  x  2.50 

4.  Loss  from  bends.      The  descending  passage  joins 
the  horizontal  one  by  a  curve  whose  radius  of  curvature 
cannot  much  exceed  the  radius  of  the  circular  passage. 
In  this  case  we  may,  according  to  Weisbach,*  put  the  loss 

of  head  =  head  due  velocity  = i.oo 

*  Mechanics,  Coxe's  Translation,  1870,  vol.  I.  p.  898. 


HYDRAULIC   COMPRESSION  OF  AIR.  475 

The  other  bend  may  have  a  longer  radius,  and  the 
loss  need  not  exceed o.  50 

5.  Loss  from  the  slip  of  the  air-bubbles,  i.e.,  from 
their  velocity  of  descent  falling  short  of  the  velocity  of 
the  water.  It  was  a  fair  inference  from  the  experiments 
at  Minneapolis,  in  1880,  that  bubbles  of  air,  such  as 
result  from  commotion,  tend  to  rise  with  a  velocity  not 
exceeding  0.80  foot  per  second.  In  fact  this  figure  is 
probably  in  excess,  since  their  velocity  is  as  the  square 
root  of  their  diameter,  and  their  diameter  diminishes  as 
they  descend.  The  percentage  of  loss,  therefore,  from 
this  source  is  0.8/8  =  10  per  cent,  which  represents  a 
head  of. 2.40 

We  have  therefore  a  total  loss  thus  far  of. 6.00 

which  is  25  per  cent  of  the  total  head,  but  this  is  not  the  whole 
loss. 

Loss  due  to  Solution  of  Air. — We  must  now  consider 
another  loss  of  a  more  complex  character  resulting  from  the 
physical  relations  of  air  and  water.  At  a  temperaure  of  32°  F. 
a  cubic  foot  of  water  in  contact  with  air,  at  any  pressure  what- 
ever, dissolves  .049  of  the  oxygen  and  0.0235  of  the  nitrogen 
contained  in  a  cubic  foot  of  the  air.  These  gases  so  dissolved 
appear  to  assume  the  liquid  form  and  remain  inseparable  from 
the  water  so  long  as  the  pressure  and  temperature  continue. 
A  change  of  temperature,  within  the  natural  range  does  not 
affect  the  phenomenon  materially.  A  diminution  of  pressure 
leads  to  immediate  elimination  of  air  in  the  form  of  bubbles  so 
minute  that  they  are  only  discernible  as  a  milky  hue  in  the 
water.  The  oxygen  forms  substantially  0.21  and  the  nitrogert 
0.79  of  the  atmosphere,  so  that  each  cubic  foot  of  water  takes 
up  and  holds  in  solution  0.049  X  0.21  -f-  0.0235  X  0.79  = 
0.0288  cubic  foot  of  air  under  whatever  pressure  the  air  may 
be.  This  law,*  it  may  be  remarked,  has  not  been  verified  by- 
experiment  at  pressures  above  two  atmospheres,  but  all  analogy 


'  Roscoe  and  Schorlemmer's  Chemistry,  1894,  vol.  I.  p.  284. 


476  THE  POWER-HOUSE. 

would  lead  us  to  suppose  that  it  holds  good  for  higher  pressures, 
and  we  shall  consider  the  subject  on  that  assumption. 

The  water  carrying  the  air  down  the  shaft  is  in  a  condition 
eminently  favorable  to  the  absorption  of  the  latter,  and  we 
must  assume  that  it  passes  the  air-chamber  with  all  the  air  in 
solution  that  it  can  hold  at  that  pressure.  Under  a  pressure 
of  100  pounds  net  and  temperature  of  32°  F.,  air  weighs  at  the 
rate  of  1.59  cubic  feet  per  pound,  and  a  cubic  foot  of  water 
would  contain  0.0288/1.59  =  0.0181  pound  of  air.  We  have 
seen  (Table  9)  that  I  pound  of  air  per  second  at  100  pounds 
corresponds  to  96.5  h.p.,  therefore  each  cubic  foot  per  second 
carries  past  the  air-chamber  air  representing  96.5  X  0.0181  = 
1.75  h.p.  At  one-half  the  pressure  the  quantity  of  air  by 
weight  would  be  but  half  as  great,  and  being  under  but  half  the 
pressure  would  represent  but  one-fourth  the  power.  We  may 
therefore  assert  that  the  power  represented  by  the  air  carried 
off  uselessly  is  as  the  square  of  the  pressure  and  is  independent 
of  the  working-head. 

But  the  air  thus  compressed  without  result  is  by  no  means 
to  be  accounted  as  a  loss.  Air  is  carried  down  the  descending 
shaft  at  the  expense  of  the  working-head  until  it  dissolves  in 
the  water.  It  passes  the  air-chamber,  and  in  the  ascending 
shaft  is  eliminated  in  the  same  order  as  it  dissolves  in  1he 
descending  shaft,  and  it  aids  the  movement  in  ascending  as  it 
retards  it  in  going  down.  Its  effect  would  be  null  if  the  energy 
exerted  by  it  in  rising  were  equal  to  that  expended  on  it  while 
going  down.  To  the  extent  that  the  former  falls  short  of  the 
latter,  the  action  involves  a  loss. 

When  the  air  starts  on  its  descent,  that  portion  destined  for 
solution  in  common  with  the  rest,  undergoes  a  loss  at  the  rate 
of  10  per  cent.  The  loss  on  this  portion  diminishes  as  the  air 
enters  into  solution,  and  at  the  bottom  of  the  shaft  ceases 
entirely.  We  may  therefore  put  the  average  loss  during  the 
descent  of  the  air  at  5  per  cent.  During  the  ascent  of  the 
water  the  loss  is  represented  by  the  excess  of  the  velocity  of 
the  air  over  that  of  the  water;  that  is,  by  the  ratio  of  the 


If  YD  £  A  ULIC  COMPRESSION  OF  AIR.  477 

velocity  with  which  the  eliminated  air-bubbles  rise  in  still  water 
to  the  velocity  of  the  water.  The  velocity  with  which  air- 
bubbles  rise  is  approximately  as  the  square  root  of  their 
diameter.  Bubbles  resulting  from  commotion  are  perhaps 
\  inch  in  diameter.  Those  resulting  from  elimination  are  im- 
measurably small — less  than  Ti(r  of  an  inch  at  any  stage  of 
their  ascent.  Therefore,  if  the  former  rise  0.8  foot  per  second, 
the  latter  cannot  rise  more  than  2  inches.  These  considera- 
tions would  indicate  a  loss  near  the  efflux  of  ^,  say  2  per 
cent.  The  loss  being  o  at  the  bottom,  the  average  is  I  per 
cent.  We  are  not  far  wrong,  therefore,  in  putting  the  total  loss 
due  to  solution  of  air  at  6  per  cent  of  the  power  represented  by 
the  air  which  enters  into  solution.  In  the  case  supposed  the 
dissolved  air  represents  1.75  h.p.  per  cubic  foot  of  water  per 
second,  and  the  loss  is  0.06  X  i-75  ^  0.105  h.p.  With  an 
efficiency  of  0.75,  i  cubic  foot  per  second  on  a  head  of  12  feet 
is  about  i  h.p.  The  loss  therefore  represents  a  head  of  0.105 
X  12=  i .  26  feet  of  head,  and  the  total  efficiency  of  the  system 
is  (24  -  7.26)724  =  69.75  Per  cent. 

The  power  represented  by  the  dissolved  air  being  as  the 
square  of  the  pressure,  the  loss  due  to  solution  follows  the 
same  proportion.  For  a  pressure  one-half  that  assumed  above, 
other  elements  being  unchanged,  the  loss  would  be  0.31  5  foot; 
for  double  pressure  over  5  feet.  Should  pressures  of  400  or 
500  pounds  be  attempted  this  loss  would  assume  overwhelming 
proportions. 

The  statement  that  the  power  represented  by  the  dissolved 
air  is  as  the  square  of  the  pressure,  though  sufficiently  near  the 
truth  for  our  present  purpose,  is  not  strictly  correct,  because 
the  power  represented  by  a  given  weight  of  air  at  100  pounds 
is  not  twice  as  great  as  at  50. 


CHAPTER    XXIII. 
MEASUREMENT  OF  WATER. 

IN  the  execution  of  projects  for  development  of  water- 
power,  and  in  the  control  and  management  of  water-powers, 
the  necessity  is  constantly  arising  for  determining  quantities  of 
water.  The  measurement  of  the  absolute  volume  of  water  in 
a  reservoir  of  any  kind  is  a  matter  of  little  difficulty,  being  a 
simple  geometrical  computation.  The  question  is  usually  as 
to  the  flow  of  water,  i.e.,  the  quantity  of  water  passing  a  fixed 
point  in  a  given  time,  involving  the  unit  of  time  as  well  as  the 
unit  of  volume.  The  second  is  usually  taken  as  the  unit  of 
time,  and  the  cubic  foot  as  the  unit  of  volume,  in  all  questions 
relating  to  water-power,  the  problem  being  to  determine  the 
number  of  cubic  feet  of  water  flowing  in  one  second.  Two 
general  classes  of  methods  are  available :  I .  The  quantity  of 
water  flowing  in  a  channel  is  determined  when  the  cross -sec- 
tion of  the  channel  and  the  average  velocity  are  known,  the 
quantity  being  the  product  of  these  two.  In  operations  of  this 
class  the  important  point  is  the  accurate  measurement  of 
velocities.  2.  When  water  can  be  discharged  through  an 
orifice  either  closed  on  all  sides  or  open  at  the  top,  in  which 
latter  case  it  is  called  a  weir,  the  size  of  the  orifice,  the  head 
acting  thereon,  and  certain  modifying  conditions  determine  the 
quantity  of  water.  The  critical  part  of  such  measurements  is 
the  accurate  determination  of  the  head  which  generates  the 
velocity. 

Measurement  of  Velocities.  Floats. — An  approximate 
idea  of  the  flow  of  a  natural  stream  may  be  obtained  by  surface- 
floats,  that  is,  by  placing  in  the  water  chips  of  wood  or  any 

478 


FLO  A  7\S.  479 

objects  that  will  float,  and  observing  the  time  occupied  in 
traversing  a  given  distance.  These  observations,  combined 
with  soundings  and  measurements  for  determining  the  cross- 
section  of  the  stream  at  the  place,  will  give  the  means  of 
ascertaining,  with  an  approach  to  accuracy,  the  quantity  of 
water  flowing. 

Surface-floats  give  the  velocity  at  the  surface  of  the  stream. 
In  point  of  scientific  nicety  the  float  takes  a  velocity  a  little 
greater  than  that  of  the  water  at  the  surface.  To  understand 
how  this  may  be,  suppose  a  stream  with  an  inclination  of  i  foot 
in  a  mile.  If  we  could  suppose  the  water  to  stand  at  this 
inclination  without  motion,  we  can  readily  see  that  a  float  placed 
in  it  would  move  down-stream.  The  inclination  of  the  surface 
is  a  force  tending  to  produce  motion,  and  a  floating  body  obeys 
any  force  that  acts  on  it,  however  slight.  Now  the  forces  act- 
ing to  give  motion  to  the  float  would  not  be  affected  by  the 
movement  of  the  water.  Therefore  the  float  will  take  a 
velocity  somewhat  in  excess  of  that  of  the  water  in  which  it 
floats.  Practically  it  is  not  necessary  to  take  account  of  this 
refinement,  and  we  may  regard  the  velocity  of  the  float  as 
representing  that  of  the  water;  but  it  is  very  necessary  to 
remember  that  the  surface  velocity  is  considerably  in  excess  of 
the  average  velocity  of  the  stream.  The  average  velocity  in 
any  vertical  line  is  generally  from  80  to  90  per  cent  of  the  sur- 
face velocity.  The  surface  velocity  in  midstream  is  also  con- 
siderably in  excess  of  that  nearer  the  shores. 

Submerged  Floats  or  Double  Floats. — To  determine  the 
velocity  at  depths  below  the  surface,  observers  have  often  used 
a  float  susceptible  of  sinking,  but  maintained  at  the  desired 
depth  by  a  cord  attached  to  a  surface-float,  the  velocity  of 
which  is  assumed  to  represent  that  of  the  submerged  float. 
Within  moderate  limits  this  assumption  can,  no  doubt,  be 
admitted,  but  it  is  sometimes  carried  to  an  unwarrantable  length. 
For  instance,  in  the  early  surveys  of  the  Mississippi,  where  the 
cord  uniting  the  submerged  with  the  surface  float  presented 
more  surface  to  the  action  of  the  current  than  the  float  itself, 


480  MEASUREMENT  OF    WATER. 

the  assumption  becomes  entirely  untenable.  Such  are  the 
resources  of  modern  engineering  that,  except  for  very  approxi- 
mate operations,  floats  whether  double  or  single  need  not  be 
used  beyond  very  moderate  depths.  There  is  a  certain  advan- 
tage in  mid-depth  floats,  for  the  reason  that  the  ratio  of  the 
mean  to  the  mid-depth  velocity  is  more  free  from  uncertainty 
than  its  ratio  to  the  surface  velocity.  The  mean  velocity  in 
any  vertical  may  be  taken  at  95  per  cent  of  the  mid-depth 
velocity.  The  mid-depth  velocity  moreover  is  entirely  free  from 
the  influence  of  wind,  whereas  the  surface  velocity  is  much 
affected  by  that  cause.  In  measurements  on  such  small 
streams  as  usually  come  under  the  notice  of  the  engineer  in 
questions  of  water-power  and  water-supply,  the  writer  finds 
nothing  better  for  the  submerged  float  than  a  potato  united  by 
a  fine  cord  with  a  block  of  dry  pine  wood  i£  inches  square  and 
£  inch  thick.  The  former  is  heavier  than  water,  but  not  enough 
so  to  require  a  large  block  of  wood  to  sustain  it.  Where  the 
distance  becomes  great  enough  to  make  the  surface-float  indis- 
tinct, it  can  be  made  conspicuous  by  inserting  a  peg  carrying 
a  bit  of  red  cloth  or  paper. 

Mode  of  Measuring  a  Natural  Stream  by  Floats.— Find  a 
straight  and  regular  reach  of  the  stream  with  a  gentle  uniform 
current,  not  obstructed  by  rocks,  weeds,  drift,  or  overhanging 
trees.  Measure  a  base  line,  parallel  to  the  course  of  the 
stream  and  as  near  the  same  as  convenient.  This  need  not 
exceed  the  width  of  the  stream  in  any  case,  and  for  large 
streams  is  much  less  than  the  width.  For  the  sake  of  a  definite 
rule,  make  it,  say,  five  times  the  square  root  of  the  width.  Mark 
the  extremities,  and  lay  oft*  at  each  a  line  at  right  angles  to  the 
base  reaching  across  the  stream  (Fig.  217).  These  are  called 
the  upper  and  lower  transit  lines.  On  these  lines  stretch  cords 
across  the  stream,  and  affix  tags  of  tin  or  pasteboard  to  the 
latter  at  convenient  intervals,  each  tag  bearing  a  number 
showing  its  distance  from  the  left  bank,*  the  base  being  prefer- 

*  In  speaking  of  the  right  or  left  bank  of  a  stream  the  observer  is  sup- 
posed to  be  facing  down-stream. 


MODE    OF  MEASURING   A    NATURAL   STREAM.         481 

ably  on  the  right  bank.  Measure  the  depth  at  each  tag. 
Take  the  average  of  each  two  corresponding  depths  and  there- 
with draw  a  profile  or  cross-section  of  the  bed,  as  in  Fig.  218. 


FIG.  217. 


FIG.  218. 

The  assistant  who  launches  the  floats,  from  a  boat  or  wading, 
has  these  soundings  and  adjusts  each  float  to  mid-depth.  He 
also  observes  the  distances  at  which  each  float  passes  the 
transit  lines.  It  is  not  worth  while  to  take  the  trouble  of 
recovering  these  floats  after  passing  the  lower  transit.  The 
assistant  who  keeps  the  record  notes  the  time  occupied  by  the 
float  in  passing  the  transit  interval,  and  when  this  is  recorded 
he  receives  from  the  other  assistant  the  distances  and  records 
the  same.  The  recording  assistant  is  preferably  provided  with 
a  stop-watch,  but  an  expert  observer  can  do  very  well  with  a 
common  watch  beating  four  times  a  second,  by  keeping  the 
watch  to  his  ear  and  counting  the  beats.  The  following  table 
in  connection  with  Figs.  218  and  219  shows  the  record  and 
computation  of  such  a  measurement.  The  diagram  Fig.  219 
is  plotted  with  the  distances  in  col.  6  as  abscissas  and  the 
velocities  in  col.  8  as  ordinates.  Col.  10  contains  the  velocities 
read  from  the  diagram  for  each  5  feet  of  width,  though  for 


482 


MEASUREMENT  OF   WATER. 
TABLE   16. 


I 

a 

3456 

7 

8 

9 

10 

„ 

i 

Distance  from  Left  Bank. 

.a  c   . 

u       -' 

1--  . 

S« 

o 

E 

A! 

"S  1$ 

«i 

^  v  a 

^  1 

^>^ 

•3 
| 

js 

i 

|f 

tj 

§-S 

>1 

Itj 

!!!! 

3 

5-1 

1 

^H 

i 

aj      &4 

11 

II  -^ 

•-   u        •" 

y-"  si^ 

g|s 

z 

G 

- 

< 

* 

s 

p          u 

> 

£ 

> 

Q 

i 

0.6 

5-0 

3-3 

4.8 

4.3 

36.4 

1.37 

3-25 

•30 

4.22 

8.25 

•43 

1  1.  So 

2 

0.8 

15 

16 

13-3 

14.6 

33.7 

i.48 

9-25 

•47 

13.60 

IO.OO 

•49 

14.90 

3 

1.5 

25 

27.1 

22.6 

24.8 

34-0 

i-47 

13.25 

•47 

19.48 

I 

14.00     .44 

20.16 

4 

1-3  |  35 

34-2 

36.3 

35.2 

32-9 

1.52 

13-25     -46 

19-34 

14.25      .60 

22.80 

5 

1.6      45 

42.2 

49.6 

45-9 

27.5 

1.82 

15-50,    .74 

26.97 

15-50:      .86 

28.83 

6 

i-7      55 

52-3 

55-1 

53-7 

25-i 

1.99 

16.25      -97 

32.01 

i8-75;      .07 

38.81 

7 

2-5  1  65 

67.1 

62.3 

64.7 

22.4 

2.23 

22.50      .21 

49-72 

27-50      -23 

61.32 

8 

2.4 

75 

72.9 

78.3 

75-6 

24.6 

2.03 

27.00      .13 

57-51 

24.50      .97 

48.26 

9 

1.8      85       1  85.0 

87.6 

86.3 

29.1 

1.72 

21.75 

.86 

40-45 

14.25       .66 
5.oo|     .30 

23.65 
6.50 

Aggregate  uncorrected  discharge.  '. 


540.33 


True  discharge  of  stream  540.33  X  0.95  =  513.31  cubic  feet  per  second. 

to  each    single   foot, 
to  which  each  velocity 


greater   exactness   they  might  be   read 
Col.  9  contains  the  area  of  cross-section 


^^ 

^ 

^ 

.^—  -  • 

^  —  • 

1  —  v 

% 

^ 

\ 

FIG.  219. 

in  col.   10  may  be  supposed  to  apply,  and  col.  n  the  product 
of  the  corresponding  quantities  in  9  and  10,  being  the  uncor- 


MODE    OF  MEASURING  A    NATURAL  STREAM.        483 

rected  quantity  of  water  passing  the  partial  areas.  The  aggre- 
gate of  col.  1 1  is  multiplied  by  0.95  for  the  true  discharge  of 
the  stream.  In  the  application  of  floats  to  deep  and  wide 
rivers,  too  wide  to  distinguish  the  float  with  the  naked  eye,  and 
especially  to  navigable  rivers,  the  transit  lines  cannot  be 
marked  by  ropes  or  cords.  In  lieu  of  these  a  theodolite  is 
positioned  at  each  end  of  the  base  line  and  is  used  to  mark  the 
transits  and  positions  of  the  floats.  The  base  line  here  has  a 
length  of  100,  200,  or  300  feet.  The  floats  are  launched  from 
a  boat  anchored  in  the  stream,  and,  if  they  are  too  elaborate 
and  expensive  to  be  sacrificed,  a  second  boat  is  kept  in  waiting 
below  to  pick  them  up.  When  the  float  is  launched  and 
approaches  the  transit  line,  the  up-stream  observer  has  his 
instrument  clamped  on  that  line;  the  down-stream  observer 
keeps  his  instrument  focussed  on  the  float.  When  the  float 
crosses  the  line  the  up-stream  observer  utters  a  shout.  There- 
upon the  down-stream  observer  reads  the  angle  which  deter- 
mines the  position  of  the  float  at  its  upper  transit,  and  the  time- 
keeper starts  his  stop-watch.  The  down-stream  observer  then 
clamps  his  instrument  on  the  lower  transit  line,  and  the 
up-stream  observer  focusses  his  instrument  on  the  float.  At 
the  down-stream  transit  the  down-stream  observer  utters  a 
shout,  the  up-stream  observer  reads  his  angle  and  the  time- 
keeper stops  his  watch,  etc.  The  time-keeper  may  be  charged 
with  the  duty  of  recording  all  the  observations,  though  this  is 
sometimes  made  the  duty  of  a  separate  assistant.  A  system 
of  signals  is  used  for  communicating  with  the  boats.  The 
submerged  is  connected  with  the  surface  float,  preferably  by  a 
copper  wire,  presenting  but  little  surface  to  the  current,  and 
special  devices  are  necessary  in  launching  the  float  to  prevent 
the  latter  from  becoming  kinked  and  snarled.  In  the  Missis-r 
sippi  River  Survey  of  1850-60,*  the  submerged  floats  were 
kegs  without  top  or  bottom,  6  to  12  inches  diameter  and  9  to 
15  inches  high,  weighted  with  hoops  of  lead.  The  surface- 


*  Report  of  Humphreys  and  Abbott,  1861,  p.  224. 


484  MEASUREMENT   OF    WATER. 

floats  were  6  or  8  inches  diameter,  3  inches  deep,  of  cork  or 
pine  wood.  Sometimes  tin  vessels  were  used  of  ellipsoidal 
shape.  They  were  connected  with  the  submerged  float  by 
cords  one  to  two  tenths  of  an  inch  diameter. 

Floats  reaching  nearly  to  the  bottom  of  the  channel  are 
used  in  artificial  channels  of  uniform  depth.  They  consist  of 
loaded  poles  or  of  closed  hollow  tubes  carrying  heavy  weights 
at  the  lower  end.  Preferably  they  are  stout  tubes  of  tin 
2  inches  diameter,  loaded  with  lead  to  give  them  the  desired 
immersion.  The  upper  end  projects  6  or  8  inches  above  the 
water,  and  is  closed  with  a  cork ;  this  part  is  painted  red  to 
make  it  conspicuous,  and  bears  figures  indicating  its  effective 
length,  i.e.,  its  depth  of  flotation.  This  method  is  used  where 
water-measuring  is  carried  on  in  a  regular  and  systematic 
manner  as  incidental  to  the  control  and  distribution  of  water- 
power.  A  portion  of  the  channel  through  which  the  water 
reaches  its  destination  is  fitted  with  smooth  vertical  and  parallel 
sides,  and  level  bottom  of  planking.  This  is  called  a  measur- 
ing-flume. The  transit  lines  are  marked  by  square  timbers 
laid  across  the  flume,  the  up-stream  face  vertical  and  marked 
with  conspicuous  figures  showing  distances  from  left  side  of 
flume.  To  facilitate  computations  of  velocity  the  interval 
between  the  up-stream  faces  is  accurately  adjusted  to  a  round 
distance  of  50,  80,  or  100  feet.  A  foot-bridge  consisting  of 
two  square  timbers  is  laid  some  1 5  feet  above  the  upper  transit, 
and  another  the  same  distance  below  the  lower  one.  The 
upper  bridge  also  carries  figures  indicating  distance  from  left 
side.  To  conduct  such  a  measurement  requires  four  persons: 
i .  The  person  in  charge  of  the  work,  who  is  supposed  to  be  a 
trained  assistant;  2.  An  intelligent  workman  who  launches 
the  floats;  3.  A  laborer  who  catches  the  floats  and  removes 
them  from  the  water;  4.  A  laborer  who  takes  the  floats  from 
No.  3  and  carries  them  to  No.  2.  A  gauge  at  the  flume  shows 
the  height  of  water  and  indicates  the  length  of  tube  required. 
Assistant  No.  L  places  himself  at  the  up-stream  transit  on  the 
right  bank.  Stop-watch  and  note-book  in  hand,  pencil  in 


SO  UKCES   OF  EKKOX.  48  5 

mouth ;  the  note-book  ruled  with  appropriate  columns,  the  date, 
time  of  commencement,  height  of  water,  and  length  of  tube 
used  entered  therein.  Assistant  No.  2  on  the  upper  bridge 
launches  the  floats  at  regular  intervals,  guided  by  the  figures 
on  the  bridge.  This  is  a  movement  requiring  some  skill. 
Facing  down-stream  and  resting  on  his  knees,  he  passes  the 
tube  into  the  water  in  a  slanting  direction,  throwing  the  bottom 
end  well  up-stream  under  the  bridge,  holds  it  by  the  top  till 
the  current  brings  it  into  an  erect  position,  then  abandons  it, 
being  careful  to  release  it  at  its  proper  depth  of  immersion, 
otherwise  it  would  oscillate  and  perhaps  strike  the  bottom. 
No.  I  starts  his  watch  at  the  crossing  of  the  upper  transit, 
records  the  distance  of  the  tube  from  the  left  side,  which  is 
called  to  him  by  No.  2,  and  walks  briskly  to  the  lower  transit 
station.  He  stops  his  watch  when  the  float  crosses  the  lower 
transit,  and,  after  he  has  recorded  the  time  interval,  receives 
from  No.  2,  and  records,  the  distance  from  the  left  side  at  the 
lower  transit;  then  returns  to  the  upper  station.  Where  the 
velocity  exceeds  5  feet  per  second  this  method  becomes  too 
trying  for  No.  I ,  and  it  is  better  to  have  a  fifth  man  to  keep  the 
record. 

Sources  of  Error  in  Measuring  with  Loaded  Tubes. — Mr. 
James  B.  Francis,*  who  developed  and  applied  this  method  in 
the  management  of  the  Lowell  Water-power,  examined  care- 
fully the  several  circumstances  which  tend  to  make  the  velocity 
of  the  tube  different  from  that  of  the  water  in  which  it  floats. 
These  are: 

I.  In  the  most  regular  channel  the  length  of  the  tube  is 
less  than  the  depth  of  the  water.  In  an  irregular  channel  or 
one  liable  to  have  deposits  and  obstructions  this  difference  is 
considerable.  The  slowest-moving  water  does  not  have  its  full 
effect  upon  the  velocity  of  the  tube,  and  the  latter  is  somewhat 
greater  than  that  of  the  water.  As  the  result  of  a  long  series  of 
experiments,  Mr.  Francis  determined  the  following  correction 
for  this  source  of  error : 

*  Lowell  Hydraulic  Experiments,  1867. 


486  MEASUREMENT  OF   WATER. 

Let  d  be  the  depth  of  water  and  dl  the  immersion  of  the 

tube; 

qv  the  quantity  of  water  as  determined  by  the  floats  ; 
q  the  corrected  quantity.      Then 


.      .      (66) 

This  formula  was  later  revised  by  Mr.  Francis,  and  appears  in 
the  fourth  edition  of  his  work  under  the  following  form  : 


q  =  q  [\.012  -0.116*7 j-L],        .      .      .      (67) 


2.  The  velocity  of  the  filaments  of  water  below  the  surface 
does   not  diminish   uniformly  with  the   depth.      The   pressure 
exerted  by  moving  water  .on  a  solid  body  is  not  proportional 
to  the  velocity,  but  rather  to  the  square  of  the  velocity.      It 
results   from   these   laws   that,    while    the    float  takes   such   a 
velocity  as  equalizes  the  pressure  on  opposite  sides  of  it,  it  does 
not  take  the  mean  velocity  of  the  water  in  which  it  is  immersed. 
Mr.  Francis  finds  from  a  mathematical  investigation  that,  when 
the   mean  velocity  of  the  water  is  2.6  feet  per   second,  the 
velocity  of  the  tube  would  fall  short  of  that  of  the  water  by 
about  the  -fa  part. 

3.  For    the    reason    already   alluded    to    (page    479)    the 
velocity  of  the  float  would  tend  to  exceed  that  of  the  water. 
The  labors  of  physicists  who  have  investigated  this  question 
show  that  in  the  case  supposed  this  tendency  would  be  equal 
to  the  -fa  part  of  the  mean  velocity  of  the  water.      That  is, 
Nos.  2  and  3  would  practically  offset  each  other. 

4.  A  heavy  body  suddenly  immersed  in  water  and  floating 
therein  does  not  instantly  acquire  the  velocity  of  the  latter. 
Its  inertia  must  be  overcome  by  the  pressure  which  the  water 
exerts  on  it  in  virtue  of  its  relative  velocity,  and  this  pressure 
becomes  less  and  less  as  the  velocity  of  the  body  approaches 
that  of  the  water.     In  fact,  mathematical  analysis  indicates  that 


SOURCES   OF  ERROR.  487 

the  float  never  acquires  the  velocity  of  the  water,  though  it 
continually  approaches  the  same. 

The  result  of  Mr.  Francis's  inquiry  is  that  if  we  suppose  the 
tube  to  be  placed  in  moving  water  and  held  at  rest,  then  sud- 
denly released,  it  will,  after  moving  20  feet,  have  a  velocity 
^  part  less  than  that  of  the  water,  the  latter  being  as 
formerly  supposed.  The  supposition,  however,  of  starting 
from  rest  has  no  application.  The  tube  is  placed  in  the  water 
in  a  much  inclined  position,  generally  nearer  horizontal  than 
vertical.  It  is  held  by  the  top  till  it  comes  into  a  vertical 
position.  When  it  comes  into  that  position  the  centre  of 
gravity  of  the  tube,  which  is  near  the  lower  end,  is  moving 
faster  than  the  water.  We  may  therefore  neglect  this  source 
of  retardation  and  conclude  that  No.  I  is  the  only  source  of 
inaccuracy  that  need  be  taken  account  of. 

It  is  only  in  certain  situations  that  floats  can  be  employed. 
In  a  closed  conduit  they  are  obviously  inapplicable,  and  in  an 
open  channel  they  require,  for  the  accurate  determination  of 
the  velocity,  a  considerable  length  of  channel,  which  it  is  often 
difficult  to  obtain.  In  any  case  they  require  a  degree  of  regu- 
larity in  the  channel  not  always  to  be  found.  It  is  often 
necessary,  therefore,  to  infer  the  velocity  from  effects  other  than 
the  transportation  of  floats.  Among  these  effects  are:  I.  The 
pressure  of  the  current  on  a  square  or  round  disk  placed  normal 
to  the  direction  of  the  current.  This  pressure  is  supported  by 
a  spring  and  is  measured  by  the  extent  to  which  the  latter  is 
deflected.  2.  A  round  metallic  ball,  supported  by  a  wire,  is 
immersed  in  the  current,  and  the  velocity  is  ascertained  from 
the  angle  of  inclination  which  the  wire  takes  under  the  com- 
bined action  of  gravity  and  pressure  of  water.  If  oc  be  .the 
angle  between  the  wire  and  the  vertical,  and  w  the  weight  of 
the  ball,  the  pressure  of  the  water  will  be  represented  by 
•w  sin  a.  No  practical  method  of  water-measurement  has  been 
developed  on  the  line  of  i  or  2,  but  2  would  probably  be  found 
to  present  as  few  difficulties  of  application  and  as  few  sources 
of  error  as  any  method  in  use.  3.  Vanes  fixed  upon  a  rotating 


488  MEASUREMENT  OF   WATER. 

axis  cause  it  to  revolve  under  the  action  of  the  current  with  a 
velocity  bearing  to  that  of  the  current  a  certain  fixed  relation, 
which  must  be  determined  by  experiment.  This  principle  has 
received  wide  application  in  the  current-meter,  which  has 
latterly  been  more  and  more  taking  the  place  of  other  modes 
of  velocity  measurement.  4.  A  vertical  tube  bent  to  a  right 
angle  at  its  lower  end,  and  immersed  in  the  water,  will,  when 
the  horizontal  extremity  is  turned  toward  the  current,  be  filled 
to  a  height  above  the  hydrostatic  level.  When  turned  in  the 
reverse  direction  the  water  in  the  tube  sinks  below  the  same 
level.  From  the  elevation  or  the  depression,  or  from  a  com- 
bination of  the  two,  the  velocity  is  determinable.  An  instru- 
ment founded  on  this  principle,  called  the  Pitot  tube,  has  been 
much  employed  in  the  measurement  of  velocities.  Passing  over 
methods  I  and  2,  as  mainly  speculative,  we  will  first  consider 

The  Current-meter. — This  instrument  takes  two  general 
forms,  viz.,  cup  vanes  and  helical  vanes.  In  the  first,  four 
cup-shaped  vanes,  Fig.  220,  are  arranged  around  an  axis. 
The  current  acts  upon  the  convex  side  of  the  vane  during  one- 
half  its  rotation,  on  the  concave  side  during  the  other  half. 
The  pressure  exerted  on  the  concave  side  greatly  exceeds  that 
on  the  convex  side.  The  system  of  floats  will  continue  to 
rotate  with  the  convex  side  forward.  Fig.  220  shows  a  meter 
of  this  form  as  made  by  Buff  and  Berger  of  Boston.  It  is 
shown  as  arranged  for  deep-water  observations,  being  adjusted 
upon  a  rope  suspended  from  an  anchored  boat,  and  carrying  a 
heavy  weight  which  rests  upon  the  bottom  and  keeps  a  strain 
upon  the  rope.  For  shallower  channels  the  meter  is  mounted 
on  a  rod  consisting  preferably  of  several  pieces  of  brass  tubing 
screwed  together  and  capable  of  being  separated  for  convenient 
packing  in  a  box.  The  instrument  is  shown  as  rigged  for 
registering  the  revolutions  by  electricity,  the  clockwork  and 
dial  as  well  as  the  voltaic  cell  which  generates  the  electric 
current  being  in  the  boat  or  on  the  bank.  The  electric  current 
goes  through  the  rotating  axis,  one  of  the  wires  being  held  in 
contact  with  it.  A  bit  of  non-conducting  material  is  inserted 


THE   CURRENT-METER. 


480 


in  the  axis,  and  comes  in  contact  with  the  wire  at  each  revolu- 
tion, breaking  the  circuit  and  advancing  the  prime-mover  wheel 
of  the  clockwork  by  one  tooth.  The  makers  say :  «  This  form 
was  used  upon  the  gauging  of  the  Connecticut  River  by  General 
Ellis,  and  was  designed  particularly  to  avoid  the  catching  of 
floating  substances,  such  as  leaves  and  grass,  upon  either  the 


FIG.  220. 

vanes  or  the  axis,  and  to  render  the  record  of  the  instrument 
independent  of  the  position  of  its  axis  with  respect  to  the  line 
of  the  current;  also,  to  get  less  friction  upon  the  axis  so  as  to 
measure  low  velocities  accurately. 

' '  This  current-meter  is  constructed  upon  the  principle  of 
Robinson's  anemometer,  turning  by  the  difference  of  pressures 
upon  opposite  vanes  of  the  wheel.  The  vanes  of  this  meter, 
however,  instead  of  being  hemispherical  cups  with  a  straight 
stem,  are  made  conical  at  the  ends,  and  are  made  hollow  and 
taper  to  the  central  hub,  so  as  to  offer  no  obstruction  to  the 


49°  MEASUREMENT  OF    WA7*ER, 

slipping  off  of  straws,  leaves,  or  grass  as  the  wheel  revolves. 
The  central  hub  is  made  tapering  so  that  any  object  can  slide 
off  easily,  and  it  extends  over  the  joints  at  the  ends  of  the  axis, 
so  as  to  enclose  and  protect  them  from  floating  substances. 
The  axis  runs  in  iridium  bearings.  The  forward  end  of  the 
frame  which  carries  the  wheel  can  be  turned  and  secured  in 
any  position,  so  that  the  wheel  can  be  horizontal,  vertical,  or 
at  any  desired  angle. 

"  The  electrical  connection  is  made  by  carrying  an  insulated 
wire  from  near  the  centre  of  the  instrument,  where  the  insulated 
wire  from  the  battery  is  attached  to  it  by  a  binding-screw  when 
in  use,  out  to  the  end  of  one  arm  of  the  wheel-frame,  where  it 
ends  in  a  fine  platinum  wire  resting  upon  a  ring  in  the  hub  of 
the  wheel.  This  ring  is  made  of  alternate  interchangeable 
sections  of  silver  and  hard  rubber,  secured  in  place  by  screws, 
so  that  their  position  can  be  changed  to  register  whole  or  part 
revolutions  as  desired.  There  is  also  a  socket  and  set-screw 
in  the  body  of  the  frame,  near  the  centre,  for  the  return  current, 
which  can  be  carried  through  a  plain  wire  slightly  twisted  round 
the  insulated  wire  so  as  to  form  one  cord.  If  the  instrument  is 
run  upon  a  wire  or  has  a  metallic  connection  with  the  surface, 
the  return  current  can  be  made  through  that.  A  better 
method  now  in  vogue  is  to  use  a  '  twin  '  insulated  wire. " 

Fig.  221  shows  a  current-wheel  with  helical  blades,  giving 
motion  to  a  horizontal  shaft.  The  blades  join  a  hub  on  the 
shaft,  and  are  limited  by  an  exterior  rim.  In  some  cases  this 
rim  is  made  double  and  encloses  a  vacant  space  giving 
buoyancy  to  the  wheel  and  relieving  the  bearings  of  pressure 
except  the  thrust.  The  wheel  is  encircled  by  a  stout  frame  to 
protect  it  from  injury.  A  small  bevel-gear  on  the  shaft  gives 
motion  to  a  train  of  wheelwork  enclosed  in  a  box  A  with  a 
glass  cover.  The  ratchet-wheel  shown  is  moved,  one  tooth 
at  a  time,  by  a  spring-catch  to  which  is  attached  a  cord  reach- 
ing to  the  surface  of  the  water.  A  pull  on  the  cord  throws  the 
clockwork  out  of  gear,  and  the  next  pull  throws  it  in.  The 
meter  is  shown  as  attached  to  a  rod.  The  observer  stands  on 


THE    CURRENT-METER. 


49 I 


a  bridge  or  temporary  platform  over  the  watercourse.  After 
noting  the  reading  of  the  dial  he  places  the  meter  in  the  water 
at  the  required  depth,  guided  by  a  graduation  on  the  rod,  with 
the  clockwork  out  of  gear.  An  assistant  holds  the  meter  in 


FIG.  221. 


FIG.  22ia. 


place.  A  stop-watch  is  commonly  used  for  noting  the  time, 
but  an  ordinary  watch  does  very  well.  At  the  commencement 
of  an  even  minute,  the  observer  pulls  the  string  to  throw  the 
wheelwork  in  gear.  After  the  lapse  of  a  suitable  number  of 
seconds  he  throws  it  out,  raises  the  meter,  and  notes  the  dial. 


492  MEASUREMENT  OF   WATER. 

As  indicated  by  dotted  lines  the  instrument  admits  the  attach- 
ment of  electric  wires  when  required. 

An  Acoustic  Meter. — The  writer,  while  in  the  service  of 
the  U.  S.  Engineer  Department,  had  occasion  to  observe 
the  working  of  current-meters.  He  became  convinced  that 
their  chief  source  of  difficulty  and  error  lay  in  the  means  used 
for  conveying  their  indications  to  the  observer.  Especially  is 
this  the  fact  when  the  revolving  shaft  operates  a  train  of  wheel- 
work  from  which  sediment  cannot  be  excluded.  The  attempt 
to  exclude  it  involves  the  use  of  a  stuffing-box,  which  is  in  itself 
a  source  of  uncertain  and  varying  resistance.  The  electric 
meter,  also,  owes  its  chief  difficulties  to  the  same  cause.  The 
necessity  of  being  accompanied  by  attachments  of  wire,  battery, 
and  dial  is  a  serious  limitation  on  its  usefulness,  and  the  main- 
tenance of  the  current,  unless  in  the  hands  of  trained  elec- 
tricians, is  a  source  of  continual  trouble,  vexation,  and  delay. 
It  appeared,  therefore,  that  the  meter  most  suitable  for  ordinary 
uses,  and  to  be  entrusted  to  ordinary  assistants,  would  be  the 
one  most  free  from  attachment  and  appendage.  The  ear 
appeared  to  be  just  as  accurate  a  receiver  of  these  indications 
as  the  eye,  and  the  metallic  rod  sustaining  the  meter  a  perfectly 
satisfactory  channel  for  their  conveyance.  If  a  sensitive  ear 
be  applied  to  a  hollow  brass  rod  1 5  feet  long,  it  is  hardly 
possible  to  touch  the  other  end  with  a  pin  so  lightly  that  it 
cannot  be  heard.  These  considerations  determined  the  form 
of  the  meter  to  be  used  on  the  headwaters  of  the  Mississippi. 
It  consisted  simply  of  the  wheel,  Fig.  221,  with  its  frame  and 
rod,  divested  of  gear,  ratchet,  dial,  wheelwork,  string,  and 
•wire.  The  shoulder-bearing  of  the  shaft  was  formed  as  in  the 
magnified  sketch,  Fig.  22  la,  in  a  helical  form,  so  that  the  shaft 
•carrying  the  meter  advanced  a  little  during  its  revolution  and 
at  the  completion  of  a  revolution  dropped  back,  under  the 
pressure  of  the  water,  with  a  click.  The  advance  need  not  be 
more  than  ^1T  of  an  inch.  The  click  was  more  pronounced 
than  necessary,  being  audible  50  feet  away.  There  was  no 
difficulty  in  counting  as  high  as  six  turns  per  second  or  as  low 


RATING   OF  CURRENT-METERS.  493 

as  one  turn  in  10  seconds,  the  velocity  ordinarily  met  with  in 
running  streams  being  from  one  to  three  turns  per  second. 
Several  meters  of  this  form  were  made  and  were  used  exclu- 
sively in  the  measurements  of  the  Mississippi,  Crow  Wing,  and 
St.  Croix  rivers,  which  continued  daily  from  January  I  to 
December  31,  1882.  Hardly  any  delay  was  experienced  from 
the  derangement  of  the  meters,  a  fact  which  will  be  the  more 
readily  believed  when  we  remember  that  there  was  nothing 
about  them  susceptible  of  derangement. 

Rating  of  Current-meters. — For  ordinary  purposes  the 
inclination  of  the  screw-blades  is  made  such  that  a  turn  of  the 
wheel  implies  a  movement  of  i  foot  of  the  water.  The  maker 
usually  verifies  this  adjustment,  but  it  cannot  be  depended  on 
as  permanent,  and  the  observer  cannot  feel  assured  that  wear, 
sediment,  and  the  action  of  water  will  not  change  it.  It  is 
imperatively  necessary  to  verify  or  revise  the  adjustment  from 
time  to  time.  This  is  usually  done  by  moving  the  meter  at  an 
accurately  determined  velocity  through  still  water. 

Fig.  222  indicates  the  arrangement  used  for  rating  the 
acoustic  meter  just  described.  A  round  float  was  made,  12 
feet  in  diameter,  and  capable  of  sustaining  1000  pounds  or 
more.  Across  this  was  laid  a  stout  timber  of  greater  breadth 
than  depth,  reaching  a  few  feet  beyond  the  float  on  one  side 
and  to  a  distance  of  about  16  feet  from  the  centre  on  the  other. 
The  projecting  part  tapered  to  small  dimensions  at  the  outer 
end.  The  float  was  anchored  in  the  vicinity  of  a  high  railroad 
trestle  crossing  a  stagnant  bayou  of  the  Mississippi,  by  driving 
a  stout  iron  rod  through  a  hole  in  the  timber  at  the  centre 
of  the  float,  deep  into  the  bottom.  The  rod  rose  several  feet 
above  the  water,  and  a  hollow  wooden  tube  was  slipped  over 
this  part  of  the  rod.  The  rod  rose  considerably  higher  than 
shown,  and  was  braced  from  the  trestlework.  The  bottom  of 
the  tube  was  made  fast  to  the  timber,  which  was  fastened  to 
the  float,  and  the  upper  end  carried  a  round  drum  or  pulley  on 
which  a  cord  was  wound.  This  cord  extended  horizontally  to 
the  trestlework,  passed  over  a  pulley,  and  up  to  the  bridge 


494 


MEASUREMENT  OF    WATER. 


floor,  there  over  another  pulley,  and  sustained  a  weight  as 
shown,  the  action  of  which  caused  the  float  to  revolve.  By 
changing  the  weight  the  velocity  could  be  varied  in  any  desired 
ratio.  The  observer  sat  on  the  float  near  the  middle,  counted 


FIG.  222. 

the  clicks  of  the  instrument,  and  noted  the  time  of  a  revolution. 
The  distance  of  the  centre  of  the  meter  from  the  centre  of  the 
float  was  such  that  the  former  described  exactly  100  feet  at 
each  revolution.  The  float  was  not  revolved  more  than  one 
turn  at  a  time,  as  the  rotatory  movement  imparted  to  the  water 
was  found  to  affect  the  velocity  of  the  meter  on  the  second  and 
subsequent  turns.  The  extremity  of  the  timber  carrying  the 
meter  stopped  against  a  small  wooden  bar.  It  started  when 
this  bar  was  momentarily  removed,  and  brought  up  short  against 
it  at  the  end  of  a  revolution.  100  divided  by  the  number  of 
clicks  in  a  revolution  of  the  float  represented  the  distance 


THE  PITOT   TUBE.  495 

traversed  in  one  turn  of  the  wheel.  Except  for  very  low 
velocities  it  was  found  that  the  number  of  clicks  in  a  turn  of 
the  float  was  the  same  whether  the  velocity  was  fast  or  slow. 
When  the  weight  ran  down  it  was  raised  by  revolving  the  float 
in  the  reverse  direction,  which  was  easily  done  by  the  attendant 
grasping  a  rope  attached  to  a  timber  of  the  bridge  and  walking 
on  the  circular  float. 

The  Pitot  Tube.— If  a  tube  open  at  both  ends  be  held 
vertically  in  a  running  stream,  the  water  will  stand  within  the 
tube  a  little  lower  than  outside.  If  the  lower  end  be  bent  to 
a  right  angle  and  the  horizontal  part,  called  the  ajutage,  be 
directed  up-stream,  the  water  will  stand  considerably  higher 
inside  than  outside.  If  the  ajutage  be  turned  at  right  angles 
to  the  current  or  down-stream,  the  water  will  stand  lower 
inside  than  outside.  In  each  case  the  difference  in  level 
between  the  water  inside  and  outside  the  tube  has  a  definite 
relation  to  the  velocity  of  the  current  at  the  ajutage.  As  it  is 
very  difficult  to  measure  the  level  of  water  in  a  running  stream 
with  sufficient  accuracy  for  this  purpose,  the  instrument  usually 
consists  of  two  tubes,  the  first  opening  up-stream,  the  second 
straight  and  opening  downward  or  with  an  ajutage  opening  at 
right  angles  to  the  current  or  down-stream.  The  difference  of 
level  in  these  tubes  is  a  correct  indication  of  the  velocity  of  the 
water.  The  most  important  part  of  the  instrument  consists  in 
arrangements  for  the  accurate  measurement  of  this  difference 
of  level.  These  tubes  are  of  glass  above,  joined  to  copper 
below,  the  former  being  fixed  upon  an  accurate  scale.  The 
glass  tubes  open  into  a  bulb  or  vessel  communicating  with  the 
atmosphere  through  a  cock,  and  a  cock  controls  the  access  of 
water  to  the  copper  tubes.  To  admit  of  accurate  measurement 
the  level  of  the  water  in  the  glass  tubes  is  raised  by  suction, 
the  simplest  means  being  a  nipple  or  mouthpiece  on  the  bulb 
before  mentioned,  to  which  the  mouth  is  applied.  The  lungs 
are  readily  capable  of  creating  a  vacuum  of  3  feet.  This  being 
done  and  the  bulb  excluded  from  the  air  by  the  cock,  the  two 
columns  stand  at  a  height  convenient  for  measurement,  and 


49^  MEASUREMENT   OF    WATER. 

their  relative  level  is  in  no  way  affected  since  the  pressure  of 
the  air  is  the  same  in  both.  The  measurement  is  still  further 
facilitated  by  closing  the  lower  cock  at  the  proper  moment, 
after  which  the  two  columns  are  cut-off  from  external  influence 
and  are  perfectly  still.  Accurate  observations  may  be  taken 
with  the  glass  tubes  and  bulb  wholly  immersed  in  the  water, 
in  which  case  the  air  above  the  water  is  condensed  without 
affecting  the  relative  height. 

In  this  instrument,  as  in  the  current-meter,  it  is  the  rating 
that  gives  validity  to  the  indications.  A  very  slight  difference 
in  the  ajutage  makes  a  material  difference  in  the  rating,  so  that 
the  rating  of  one  instrument  is  of  no  value  for  another.  The 
most  convenient  mode  of  rating  is  by  comparing  the  surface 
velocity  of  a  stream  as  determined  with  the  instrument  with 
the  same  as  determined  by  surface-floats,  taking  due  account 
of  the  source  of  error  in  the  velocity  of  surface-floats  already 
pointed  out  (page  479).  The  method  of  rating  by  causing  the 
instrument  to  move  in  still  water  is  more  accurate  in  theory, 
but  beset  with  greater  practical  difficulties. 

This  instrument  was  used  by  the  French  experimenters 
Darcy  and  Bazin*  in  determining  the  laws  of  fluid  motion,  and 
is  well  adapted  to  uses  requiring  extreme  nicety.  It  is  prob- 
ably not  destined  to  extensive  application  in  the  practical  work 
of  water-measurement. 

Measurement  of  Heights  of  Water.— No  operation  in 
water-power  engineering  is  more  common  or  more  necessary 
than  the  accurate  observation  of  heights  of  water.  In  measure- 
ment of  water  by  means  of  weirs  and  orifices  the  height  is  the 
main  element.  A  record  extending  over  a  period  of  years,  of 
the  height  of  water  in  a  stream,  gives  the  means  of  ascertaining 
the  flow  with  an  approximation  to  accuracy.  In  legal  ques- 
tions which  are  constantly  arising  as  to  the  flow  of  streams, 
amplitude  of  floods,  value  of  water-power,  etc.,  no  data  obtain- 
able at  equal  expense  and  trouble  are  so  valuable  as  accurate 
gauge-records. 

*  Recherches  Hydrauliques.    Paris,  1865. 


MEASUREMENT  OF  HEIGHTS  OF    WATER.  497 

A  gauge  designed  to  be  permanent  should  be  of  cast  iron, 
bolted  solidly  to  masonry  or  natural  rock.  It  should  be  5  or 
6  inches  wide  and  an  inch  thick.  As  such  gauges  are  intended 
to  be  read  by  unskilled  persons,  they  are  usually  graduated  in 
feet  and  inches  as  indicated  in  Fig.  223.  The  gauge  is  shown 


o 


FIG.  223. 


FIG.  224. 


6  inches  wide.  The  inch-marks  are  I  finches  long,  the  quarter- 
foot  marks  2,  the  half- foot  3.  The  foot-marks  extend  across 
the  face  of  the  gauge.  It  is  thus  not  necessary  to  attach 
figures  to  any  but  the  foot-marks,  the  inches  being  readily  dis- 
cerned by  the  length  of  the  marks.  Fig.  224  is  a  wooden 
gauge  graduated  in  tenths  and  hundredths.  In  marking  the 
graduation  a  line  is  drawn  I  inch  from  the  edge,  a  second 
i \  inches,  a  third  i£,  a  fourth  2.  The  hundredth  marks  extend 
to  the  first  line,  the  half-tenths  to  the  second,  the  tenths  to  the 


498 


MEASUREMENT  OF   WATER. 


third,  the  half- foot  marks  to  the  fourth,  and  the  foot-marks 
entirely  across  the  face.  The  gauge  is  generally  painted  white, 
and  the  marks  and  figures  put  on  in  black  with  a  brush,  the 
latter  with  stencil  plates.  A  more  permanent  method  is,  first, 
to  oil  the  wood,  then  cut  the  marks  with  a  sharp  instrument, 
then  rub  the  face  with  powdered  charcoal  mixed  with  oil, 
working  the  mixture  well  into  the  cuts ;  then  clear  the  surface 
with  a  plane.  For  temporary  purposes  the-  graduation  (not 
finer  than  inches  or  tenths  of  foot)  may  be  marked  with  a  hot 
iron,  using  Roman  numerals  for  figures.  This  makes  the  marks 
quite  conspicuous,  and  they  are  not  readily  obliterated. 

These  forms  of  gauges  presuppose  solid  artificial  structures 
for  their  attachment,  as  dam  abutments,  bridge  piers,  river 
walls,  etc.,  for  the  iron,  timber-work  for  the  wooden  gauges. 


FIG.  225. 

It  is  sometimes  necessary  to  conduct  temporary  or  even  long- 
continued  observation  of  heights  where  no  artificial  structure 
exists  and  where  it  is  quite  as  important  to  record  the  high  as 
the  low  stages.  A  gauge-rod,  set  up  on  the  bank  of  the 
stream  and  braced  to  stakes  and  the  like,  is  generally  found 
missing  after  any  considerable  rise  of  water,  and  never  survives 
the  running  of  ice.  Permanent  arrangements  for  observing 
the  height  of  water  in  such  situations  are  shown  at  Figs.  225 
and  226.  The  first  assumes  a  rock  formation.  Commencing 
at  the  stream,  a  little  below  low-water  level,  cut  a  channel  in 
the  rock  back  to  A,  where  a  vertical  face  of  5  feet  or  more  can 


DATUM  PLANE. 


499 


be  obtained.  Cut  such  a  face  and  bolt  on  the  gauge.  From 
the  level  of  the  top  of  A  cut  back  to  B,  and  bolt  on  another. 
From  B  go  to  C,  thence  to  D,  etc.,  till  the  highest  possible 
flood  is  covered.  The  .graduation  of  B  commences  where  A 
terminates,  C  where  B  terminates,  etc.  Fig.  226  assumes  a 
gravel  formation.  Here  we  do  not  use  a  connected  scale  of 
heights.  We  drive  down  the  iron  rods  A,  B,  C,  etc.,  each  12 
or  1 5  feet  long.  The  first  is  driven  to  a  depth  sufficient  to 
insure  that  it  will  never  be  above  water,  and  the  tops  of  the 
others  successively  about  5  feet  higher.  The  levels  are  carefully 


FIG.  226. 


taken  and  recorded.  The  heights  are  taken  by  means  of  a 
portable  graduated  rod  placed  on  the  head  of  the  iron  rod.  A 
discarded  level-rod  answers  very  well  for  this  purpose.  In 
high  water  a  skiff  is  used  to  observe  the  heights.  To  meet  the 
possibility  of  the  malicious  driving  of  the  rods,  the  levels  should 
be  repeated  at  intervals. 

Datum  Plane. In  every  water-power,  embracing  a  con- 
nected system  of  canals,  races,  ponds,  basins,  etc.,  the  levels 
should  refer  to  a  common  datum  plane,  so  that  the  elevation 
of  any  one  part  shows  its  relation  to  all  other  parts  of  the 
system.  It  is  common,  therefore,  in  such  works  to  assume  a 


5OO  MEASUREMENT  OF   WA  TER. 

certain  plane  of  reference  from  which  all  heights  are  estimated. 
This  is  generally  taken  low  enough  to  underlie  the  lowest 
point  in  any  part  of  the  system.  Until  a  recent  date  every 
water-power  and  every  hydraulic  work  had  its  own  system  of 
levels,  independent  of  all  others. 

The  important  United  States  Government  surveys,*  the 
Coast  and  Geodetic  Survey,  the  Lake  Survey,  the  United  States 
Geological  Survey,  now  reckon  their  heights  from  the  sea-level, 
and  bench-marks  in  this  system  of  levels  are  now  established 
in  all  parts  of  the  country,  generally  within  reasonable  distance 
of  every  important  hydraulic  work.  If  it  is  a  convenience  to 
know  the  relation  of  any  one  of  a  system  of  watercourses  to  all 
other  parts  of  the  same  system,  it  is  a  greater  convenience  to 
know  its  relation  to  all  other  parts  of  the  same  river  system  and 
all  other  parts  of  the  country.  The  datum,  therefore,  should 
be  determined  with  reference  to  the  sea-level.  At  elevated 
points  it  is  not  necessary  in  every  computation  relative  to  levels 
to  include  the  total  height  above  the  sea-level.  It  is  sufficient 
to  take  the  datum  plane  at  some  even  hundred,  or  some  even 
fifty,  or  some  even  ten,  feet  above  the  world's  bench-mark. 

Precise  Gauges. — When  water  stands  in  contact  with  a 
graduated  gauge  there  is  no  distinct  line  of  meeting  between 
the  water-surface  and  the  gauge-surface.  Through  the  action 
of  capillary  attraction  these  surfaces  join  in  a  curved  line 
running  up  the  face  of  the  gauge.  This  curve  obscures,  in 
some  measure,  the  height  of  the  water  so  that  the  latter  cannot 
be  estimated  within  less  than  an  eighth  of  an  inch.  For  many 
purposes  greater  accuracy  is  required, than  is  attainable  by  such 
means.  In  measuring  the  difference  of  level  between  the  two 
columns  in  the  Pitot  tube,  capillary  attraction  is  taken  advan- 
tage of.  A  ring-formed  index,  partly  encircling  the  tube, 
moves  in  contact  with  a  graduated  scale.  Capillary  attraction 
within  the  tube  gives  a  concave  form  to  the  surface  of  the 


*See  Dictionary  of  Altitudes  in  the  United  States,   Bulletin    No.   160 
of  the  U.  S.  Geological  Survey.     Washington,  1899. 


THE  HOOK-GAUGE.  50 1 

water,  and,  owing  to  the  reflection  of  light,  the  vertex  of  this 
cavity  is  very  distinct,  so  that  it  is  easy  to  adjust  the  index  to 
the  exact  height  of  this  vertex  and  read  the  height  on  the  scale. 

The  Hook-gauge,  Figs.  227  and  228,  is  an  instrument 
invented  by  Mr.  U.  A.  Boyden,  and  used  by  Mr.  J.  B.  Francis 
in  experiments  and  general  water-measuring  operations.  A 
graduated  rod  carries  a  hook  turning  upward,  with  a  sharp 
point.  This  hook  being  placed  below  the  surface,  and  drawn 
up  by  a  screw  motion,  when  the  point  touches  the  surface  it 
creates  a  slight  distortion  and  a  change  in  the  direction  of 
reflected  light  which  is  very  perceptible.  A  vernier  in  contact 
with  the  graduated  rod  enables  the  height  to  be  read  to  the 
nnnr  Part  °f  a  f°°t-  Neither  this  nor  any  other  precise 
method  of  determining  heights  can  be  used  upon  the  free  sur- 
face of  a  stream  or  body  of  moving  water,  owing  to  continual 
oscillations  and  disturbances.  Such  methods  must  be  applied 
to  a  limited  space  called  a  still-box,  segregated  from  the  main 
body  and  communicating  therewith  by  a  small  opening  through 
which  abrupt  oscillations  cannot  be  transmitted,  though  the 
height  of  water  is  the  same  as  the  average  height  in  the  main 
body.  The  still-box  must  be  high  enough  to  include  the 
highest  and  lowest  levels  of  the  water,  and  when,  as  usually 
happens,  the  level  is  liable  to  considerable  fluctuation,  it 
becomes,  in  the  low  stage,  a  source  of  inconvenience  by 
obstructing  the  light.  The  hook-gauge,  with  its  attachments, 
is  bolted  to  a  post  immovably  fixed  in  the  ground  or  solidly 
attached  to  a  permanent  structure. 

Fig.  229  is  an  instrument  which  the  writer  has  found  very 
convenient  for  precise  measurement  of  the  height  of  water. 
It  is  a  portable  rod  accurately  graduated,  and  is  designed  to 
measure  the  height  of  the  surface  above  an  immovable  bench, 
generally  consisting  of  an  iron  rod  driven  deep  into  the  ground 
and  surrounded  by  a  still-box.  The  latter  should  be  provided 
with  a  rest  so  that  the  rod  may  be  plumb  when  placed  in  the 
water.  A  wooden  slide  clasps  the  rod  by  means  of  light 
springs,  and  is  easily  moved  up  and  down.  The  slide  carries 


502 


MEASUREMENT  OF   WATER. 


a  lip  in  contact  with  the  rod,  and  an  index-finger  far  enough 
from  the  rod  to  touch  the  water  where  it  is  unaffected  by 


Jo 

ff. 

ft. 

WE 

—  * 

*€ 

1 

FIG.  227.  FIG.  228.       FIG.  228^. 


FIG.  229.        FIG.  230. 


capillary  attraction.  In  measuring,  the  rod  is  placed  in  the 
water  resting  on  the  bench ;  the  index-finger  is  moistened  and 
the  slide  is  pushed  down  nearly  to  the  water-surface,  or  till  it 


THE    WEIR. 


503 


almost  joins  its  image  seen  in  the  water  as  coming  up  from 
below.  Then  the  slide  is  tapped  lightly  with  a  pencil,  each 
tap  advancing  it  less  than  T^¥  of  a  foot.  When  the  index 
touches  the  water,  a  distinct  and  unmistakable  phenomenon 
occurs :  Capillary  attraction  causes  the  water  to  spring  upward 
and  a  tremor  runs  over  the  surface.  The  lip  coincides  exactly 
in  height  with  the  point  of  the  index  or  with  the  true  surface 
of  the  water.  A  vernier  reading  to  thousandths  of  a  foot  can 
be  applied  to  the  slide  if  desired,  but  it  is  hardly  necessary,  as 
the  thousandths  can  be  estimated  with  sufficient  accuracy. 

The  Weir. — Although  the  word  "weir"  or  "wear"  has 
the  general  signification  of  "  a  dam,"  its  meaning  has  latterly 
been  restricted  to  a  dam  specially  designed  to  measure  the 


FIG.  231. 

quantity  of  water  passing  over  it.  Equations  (24)  and  (28) 
relate  to  the  flow  of  water  over  dams  of  ordinary  form;  but  for 
exact  measurements  a  form  of  weir  is  presupposed  conforming 
to  that  from  which  the  formula  was  deduced.  Facilities  for 
making  such  experiments  have  multiplied  enormously  of  late, 
especially  in  scientific  schools,  and  there  is  hardly  any  form  of 
weir  or  dam  that  has  not  been  made  the  subject  of  exact 
determination  of  discharge.  We  will  adhere,  however,  to  the 
standard  form  of  measuring- weir,  Fig.  231,  presenting  a  sharp 


504  MEASUREMENT  OF   WATER. 

edge  on  the  up-stream  side,  both  on  horizontal  crest  and 
vertical  sides,  after  passing  which  the  water  leaps  freely  into 
the  air.  The  surface  of  the  water  approaching  the  weir  takes 
a  curved  form,  and  the  depth  must  be  measured  at  a  sufficient 
distance  up-stream  to  avoid  the  effect  of  this  curve.  It  is  found 
that  a  perforated  pipe  resting  on  the  bottom  of  the  channel, 
close  to  the  up  stream  side  of  the  weir  and  opening  into  a  still- 
box,  will  give,  in  the  latter,  the  true  height  of  the  surface. 
The  formula  determined  by  Mr.  James  B.  Francis  for  the  dis- 
charge of  such  a  weir  is 


Q=  3-33<X-o.  inff)H*t   .     .     .     ,     (68) 

in  which  Q  =  the  discharge  in  cubic  feet  per  second  ; 

L  =  the  length  of  the  horizontal  crest  of  the  weir  in 

feet,  the  sides  being  supposed  vertical  ; 
H  =  the  depth  in  feet,  measured  as  above  ; 
n  =  the  number  of  end  contractions  ;  that  is  to  say, 
if  the  weir  is  the  exact  length  of  the  channel 
of  approach,  there  is  no  end  contraction  and 
n  =  o  ;    if  the   weir    meets    one    side  of  the 
channel,  n  —  I  ;  if  neither  side,  n  =  2. 

The  weir  may  be  divided  into  several  parts  by  means  of 
bulkheads,  that  is,  it  may  consist  of  several  weirs  with  their 
crests  on  the  same  level,  in  which  case  n  may  be  greater 
than  2.  In  this  case  the  least  distance  between  two  weirs 
should  be  not  less  than  twice  the  greatest  depth  of  water  on 
the  weirs. 

This  formula  assumes  the  weir-opening  so  small  compared 
with  the  cross-section  of  the  channel  that  the  velocity  of 
approach  is  small,  say  not  more  than  o.  5  foot  per  second.  If 
the  water  approaching  the  weir  has  any  velocity  worth  con- 
sidering, Q  will  be  a  little  greater  than  given  by  formula  (68). 
We  must  then  find  the  head  due  the  velocity  and  add  it  to  H. 
The'n  recompute  Q  with  the  new  value  of  H.  If  we  place  the 
still-box  in  the  channel  of  approach,  and,  omitting  the  pipe, 
let  it  communicate  with  the  water  of  the  channel  by  an  orifice 


SYSTEMATIC  MEASUREMENT   OF  FLOW.  505 

in  the  up-stream  side,  we  shall  not  need,  as  a  general  thing, 
to  make  the  above  correction,  as  the  water  in  the  box  will 
stand  above  the  general  level  by  a  height  nearly  equal  to  that 
due  the  velocity  of  approach. 

When  a  weir  extends  from  side  to  side  of  the  channel,  the 
stream,  being  uncontracted  at  the  ends,  falls  in 'contact  with 
the  sides,  and  there  is  no  opportunity  for  the  admission  of  air 
under  the  sheet.  The  action  of  the  water  speedily  exhausts  the 
air  and  diminishes  the  pressure  which  opposes  the  flow,  thereby 
increasing  the  discharge  above  what  would  be  indicated  by 
the  formula.  In  order  that  the  formula  may  be  applied  with 
confidence,  means  must  be  adopted  for  giving  the  air  access  to 
the  space  under  the  sheet.  .The  weir  formula  cannot  be  applied 
with  full  confidence  to  depths  greater  than  3  feet  nor  to  depths 
more  than  one-third  the  length ;  neither  does  it  apply  where 
the  water  is  so  low  that  it  clings  to  the  weir,  on  the  down- 
stream side. 

Where  the  water  on  the  down-stream  side  rises  above  the 
crest  of  the  weir,  the  latter  becomes  a  submerged  weir  and 
the  formula  (68)  is  no  longer  applicable.  For  this  case 
Mr.  Francis  *  gives  the  following  formula : 


f),    .     .     (69) 

in  which  H  —  height  of  water  on  up-stream  side,  above  crest 

of  weir ; 
H'  =  height  of  water    on  down-stream    side,    above 

crest  of  weir. 

This  refers  to  a  weir  extending  across  the  channel.  Where 
there  are  end  contractions,  L—  o.inHmust  be  used  instead 

ofZ. 

Systematic  Measurement  of  the  Flow  of  a  Natural 
Stream.— A  single  measurement  of  the  flow  of  a  natural  stream 
has  very  little  value  unless  at  the  period  of  extreme  low  or 
extreme  high  water.  To  determine  the  average  flow  of  water 

*  Trans.  Am.  Soc.  C.  E.,  1884,  p.  312. 


5O6  MEASUREMENT  OF   WATER. 

to  be  expected  from  the  stream,  the  measurement  must  extend 
over  a  series  of  years.  How  long  a  period  must  be  taken  in 
order  to  obtain  the  true  average  cannot  now  be  stated. 
Records  ot  the  flow  of  streams  have  not  continued  long  enough 
to  enable  that  question  to  be  answered.  From  existing  in- 
formation it  appears  probable  that  the  average  flow  for  a  period 
of  twenty  years  would  not  differ  materially  from  the  average 
of  one  hundred,  and  that  the  average  of  ten  years  would  not 
differ  more  than  20  per  cent  from  the  same.  In  connection 
with  rain-gauge  records  of  long  duration,  a  single  year's 
observation  of  flow  has  a  considerable  value,  especially  if  it 
happens  to  be  a  year  of  nearly  average  rainfall.  In  what  fol- 
lows we  are  presupposing  a  series  of  daily  measurements  to 
last  at  least  a  year.  The  smaller  streams  are  most  con- 
veniently measured  by  weir.  For  the  larger  class  the  most 
suitable  instrument  is  the  current-meter. 

Measurement  by  Weir. — Figs.  18,  19,  20,  already  de- 
scribed (page  40),  show,  on  a  small  scale,  the  form  of  weir 
proper  for  a  small  stream.  The  sharp-crested  weir-plank  over 
which  the  water  flows  is  seen  at  B,  Fig.  18.  In  preparing  for 
such  measurements,  the  first  question  to  be  considered  is  as  to 
the  length  of  the  weir.  To  take  the  flow  of  20  square  miles 
of  drainage-ground  for  a  series  of  years  without  rising  more 
than  3  feet  on  the  crest  would  require  a  length  of  200  feet; 
whereas  a  length  of  20  feet  would  probably  take  the  entire  flow 
for  360  days  out  of  365.  The  case  is  not  that  of  a  permanent 
dam,  where  an  overflow  of  the  shore  connections  would  involve 
loss  of  life  and  property.  The  worst  that  could  happen  from 
overflow  would  be  the  partial  loss  of  the  weir.  The  apron  and 
sheet-piling  would  remain,  and  the  weir  could  be  put  in  order 
again  with  no  great  expense  on  subsidence  of  the  flood.  The 
practical  method  would  appear  to  be  this:  Give  the  weir  a 
length  of  not  less  than  I  foot  and  not  more  than  2  for  every 
square  mile  of  drainage-ground,  and  let  it  take  its  chance. 
Establish  ranges  and  take  the  cross-section  of  the  channel,  so 
that,  in  the  event  of  a  failure,  the  flow  during  the  continuance 


MEASUREMENT  BY  CURRENT-METER.  507 

of  the  flood  can  be  measured  by  surface  or  mid-depth  floats,  till 
the  stream  resumes  normal  dimensions,  when  the  weir  can  be 
very  readily  reestablished. 

There  would  be  no  great  chance  of  error  if  the  vertical 
sides  of  the  weir  should  rise  5  feet  above  the  crest,  provided  the 
latter  were  so  placed  that  the  weir  would  be  drowned  when  the 
water  reached  a  height  of  3  feet.  To  find  this  elevation  of  the 
crest  we  must  find  the  depth  of  a  stream  which  would  carry^the 
discharge  of  the  weir  with  the  existing  slope  and  cross-section. 

Q 


in  which  Q  =  discharge  of  weir  with  3  feet  depth  ;  A  =  corre- 
sponding area  of  cross-section;  P  =  perimeter  of  same;  and 
s  —  slope  of  surface.  Q,  c,  and  s  are  known.  From  the 
plotted  cross-section  of  the  stream-valley  P  is  found,  corre- 
sponding to  any  assumed  area  A  of  cross-section.  The 
value  of  A  can  be  found  by  trial  subject  to  the  condition 

A  3 

-    .     Having  found  A  from  the  plotted  cross-section, 


Q         I 
T^s  =V 


the  required  height  is  apparent.  This  method  requires  a  pre- 
cise gauge  on  the  up-stream  side  of  the  weir,  and  another  on 
the  down-stream  side,  the  latter  to  be  used  only  when  the  weir 
is  submerged.  Arrangements  for  measuring  the  height  of 
water  in  time  of  flood  are  shown  in  Figs.  225  and  226. 

Measurement  by  Current-meter.  —  The  best  arrangement 
for  this  case  is  to  stretch  a  wire  rope  across  the  stream.  One 
end  of  the  rope  can  usually  be  attached  to  a  tree,  the  other 
requires  an  artificial  support.  Fig.  232  shows  such  an  anchor- 
age, consisting  of  two  stout  posts  set  deep  in  the  earth  and 
supporting  a  drum  made  of  the  rough  trunk  of  a  tree.  By 
cutting  four  mortises  in  this  drum,  for  the  insertion  of  hand- 
spikes, it  becomes  a  winch  whereby  a  sufficient  strain  can  be 
brought  on  the  rope,  and  the  latter  can  be  dropped  into  the 
river  on  passage  of  boats  or  rafts.  Tags  bearing  numbers  are 
affixed  to  the  rope  at  uniform  intervals,  by  means  of  the 


506 


MEASUREMENT  OF    WATER. 


ordinary  wire-rope  clips.  In  observing  the  current  velocities 
a  boat  is  used.  This  is  made  fast  to  the  rope  at  each  of  the 
several  stations  while  the  velocities  are  being  observed, 
generally  near  the  surface,  at  mid-depth,  and  near  the  bottom. 
The  meter-rod  is  marked  with  a  scale.  The  first  reading  is 
taken  about  a  foot  below  the  surface,  the  second  as  near  the 
bottom  as  the  meter  will  run,  and  in  observing  this  the  meter- 
rod/ests  on  the  bottom.  In  this  position  the  depth  is  observed 
and  the  third  reading  is  taken  at  mid-depth.  Thus  a  complete 
cross-section  of  the  stream  is  put  on  record  at  each  measure- 


FIG.  232. 

ment.  In  some  recent  operations  of  the  Geological  Survey, 
the  observer  is  mounted  on  a  car  suspended  from  the  wire  rope 
and  running  thereon  by  means  of  grooved  wheels.  In  winter, 
as  soon  as  the  stream  freezes,  the  operation  becomes  much 
more  simple,  the  observations  being  made  through  holes  cut 
In  the  ice.  If  the  water  at  the  wire  rope  remains  long  open, 
•or  partly  open  and  partly  closed,  a  new  line  is  selected,  where 
-the  ice  is  intact  and  a  new  series  of  holes  cut.  Sometimes  a 
•covered  sledge  is  provided  mounted  on  runners  to  be  shoved 
:from  hole  to  hole.  The  holes  will  usually  be  found  freshly 
irozen  .every  cold  morning,  so  that  a  complete  outfit  must 


MEASUREMENT  BY  MEANS   OF   TURBINES.  $09 

include  an  ice-chisel,  ice-saw,  and  tongs.  A  supply  of  hot 
water  is  also  essential,  as  ice  is  liable  to  form  on  the  instrument 
whenever  it  is  withdrawn  from  the  water,  and  obstruct  its 
working.  Ice  does  not  form  on  the  meter  while  it  is  immersed 
in  water. 

Measurement  by  Means  of  Turbines. — At  great  water- 
powers,  where  it  is  necessary,  for  the  adjustment  of  rentals,  to 
keep  an  accurate  account  of  the  water  drawn  by  different 
lessees  or  users,  the  water-wheels  are  used  to  a  considerable 
extent  as  meters.  Each  wheel  is,  preferably  before  its  installa- 
tion, subjected  to  experimental  test,  to  determine  the  quantity 
of  water  discharged  under  the  varying  conditions  of  use.  The 
results  so  determined  are  arranged  in  tables  which  serve  for 
the  finding  of  the  discharge  at  any  other  time.  The  discharge 
of  a  turbine,  at  any  given  moment,  is  determined  by  three 
things :  I .  The  opening  of  the  gate  which  controls  the  dis- 
charging orifices,  called  the  speed-gate.  2.  The  head  acting 
on  the  wheel.  3.  The  velocity.  Of  course  the  discharge 
cannot  be  determined  experimentally  for  all  possible  variations 
of  these  several  elements.  It  is  determined  for  heights  of 
speed-gate  differing  so  little  that  the  intermediate  discharges 
can  be  interpolated.  These  results  are  determined  with  refer- 
ence to  the  ordinary  head  acting  on  the  wheel,  which  we  will 
call  the  "  standard  head,"  and  the  ordinary  velocity,  which 
we  will  call  the  "  standard  velocity."  The  discharge  at  each 
height  of  gate  is  also  observed  for  velocities  varying  from  the 
standard  within  the  limits  of  practice.  With  these  results  we 
are  able  to  form  a  table  giving  the  discharge  of  the  wheel  under 
the  standard  head  for  all  heights  of  speed-gate  and  all  veloci- 
ties within  the  range  of  practice.  From  this  table  the  dis- 
charge under  any  conditions  of  working  can  be  determined. 
To  fit  the  wheel  for  observing  the  several  elements  of  the 
discharge,  it  is  provided  with  a  gauge  in  the  penstock  and 
another  in  the  wheel-pit  which  serve  to  determine  the  fall  or 
head.  A  graduated  scale  is  attached  to  the  gate-rod  by  which 
the  opening  of  the  wheel-passages  may  be  observed.  The 


510  MEASUREMENT  OF   WATER. 

revolutions  of  the  wheel-shaft  per  minute  are  counted  with  the 
aid  of  a  time-keeper.  ,With  these  data,  the  discharge  of  the 
wheel  can  be  determined,  from  the  table,  for  the  observed  gate- 
opening  and  veloqity  and  for  the.  standard  head.  The  discharge 
under  the  observed  head  is  obtained  by  the  operation 

Discharge  under  observed  head 

/observed  head 
=  discharge  under  standard  head>y    standafd  head  • 

In  making  the  experiments  to  determine  the  table  of  discharge, 
the  velocity  of  the  wheel  can  be  controlled  by  a  brake  or  other 
means,  but  the  head  cannot  usually  be  closely  controlled,  and 
will  deviate  more  or  less  from  the  standard.  In  fact,  when  tl^e 
experiments  are  made  subsequent  to  installation  the  erection 
of  a  weir  in  the  race  necessarily  diminishes  the  head  largely. 
The  observed  discharge  must  in  this  case  be  reduced  to  the 
standard  head  by  the  above  method,  viz., 

Discharge  under  standard  head 


/standard  head 

=  observed  discharge  A  /  -; —      -rt 1- 

y   observed  head 

In  its  application  to  iron  wheels  this  method  is  limited  by 
the  action  of  the  water  on  the  iron.  Nodules  or  blisters  form 
on  the  surface  of  the  guides  and  floats,  partly  at  the  expense 
of  the  i*-on,  partly  from  matters  derived  from  the  water,  and 
in  the  course  of  a  few  years  materially  diminish  the  discharge. 
Little  reliance  can  be  placed  upon  this  method  without 
periodical  cleaning  of  the  surfaces,  and  even  with  this  precau- 
tion the  cleaning  leaves  the  surfaces  pitted  and  wasted  in  a 
manner  to  seriously  affect  the  discharge. 

The  Venturi  Meter. — Water-meters  for  indicating  the 
quantity  of  water  delivered  to  consumers  in  municipal  water- 
supply  systems  have  been  devised  in  innumerable  forms,  but 
with  these  devices  this  treatise  has  nothing  to  do.  It  would 
nevertheless  be  incomplete  without  some  notice  of  a  meter 
patented  and  introduced  by  Mr.  Clemens  Herschel,  which  is 


THE    VENTURI  METES.  511 

susceptible  of  use  on  a  scale  suited  to  the  requirements  of 
water-power.  It  is  called  the  Venturi  meter  because  it  is 
founded  upon  facts  in  hydraulics  to  which  attention  was  first 
called  by  Venturi,  an  Italian  physicist,  about  1796,  viz. :  Water 
moving  in  a  pipe  may  pass  from  a  condition  of  high  pressure 
and  low  velocity  to  a  condition  of  low  pressure  and  high 
velocity,  and  vice  versa,  without  great  loss  of  energy.*  In 
other  words,  pressure  and  velocity  are  mutually  convertible. 
Referring  to  Fig.  233,  suppose  CB  to  be  part  of  a  line  of 


SECTION  OF  36"VENTURI 
FIG.  233. 

pipe  which  has  its  normal  diameter  at  C  and  B,  but  between 
C  and  A  contracts  to  a  small  diameter,  and  between  A  and  B 
expands  to  normal  diameter.  Suppose  we  insert  a  small  ver- 
tical pipe  at  A ,  and  another  at  B.  The  water  while  in  motion 
will  stand  lower  at  A  than  B  by  a  height  which  we  will  call  h. 
Let  the  cross-section  at  B  be  a  times  that  at  A,  and  let  w  be 
the  weight  of  any  quantity  of  water  that  we  choose  to  consider. 

t'2 
Then  v  being  the  velocity  of  the  water  at  A ,  its  energy  is  w — , 

<?> 

w  v* 
at  B  it  is  -3  — .     That  is,  if  a  =  4,  the  energy  at  B  is  only  T^ 

t,2 

that  at  A.  What  has  become  of  the  other  f|w  ?  It  has 
be.cn  converted  into  the  head  h.  In  other  words,  the  slowing 


*  See  a  very  interesting  series  of  experiments  by  James  B.  Francis  on 
the  movement  of  water  in  expanding  tubes.  Lowell  Hyd.  Expts.  1868, 
p.  209.  The  same  principles  also  apply  to  the  Diffuser. 


$12  MEASUREMENT  OF  WATER. 

up  of  the  water  between  A  and  B  creates  a  difference  of  pressure 

a* i  vi 

represented    by   h.      We   have   therefore  w ^ =  ivh, 


whence  v 


I    2fk 

=  a\l  -%  -  . 


Of  course  the  velocity  v  could  not  be  computed  from  this 
formula,  because  it  ignores  the  frictional  head ;  but  this  result 
shows  that  the  difference  of  level  h  is  a  correct  measure  of  the 
velocity,  and  that  the  latter  can  be  determined  when  the  former 
is  known.  Practically  the  relation  between  //  and  v  is  to  be 
determined  by  experiment.  Fig.  233  shows  a  pipe  from  A, 
and  another  from  C,  though  we  have  assumed  a  pipe  from  B 
for  the  better  understanding  of  the  principle.  The  pipes  from 
A  and  C  lead  to  a  recording-instrument  which  by  means  of 
floats  and  mechanism  may  be  made  to  exhibit  upon  a  dial  the 
quantity  of  water  passing  at  any  instant,  in  cubic  feet  per 
second,  or  by  means  of  clockwork  records,  the  same  in  the  form 
of  a  diagram,  or  gives  the  aggregate  discharge  for  an  hour,  a 
day,  or  a  week. 

This  meter  can  be  inserted  in  a  line  of  penstock  to  show 
the  quantity  of  water  drawn  by  a  turbine  wheel.  It  can  be 
applied  to  an  existing  penstock  by  narrowing  the  cross-section. 
There  is  no  limit  to  the  size  of  pipes  to  which  it  can  be  ap- 
plied. In  its  application  to  water-wheels  there  is  not  neces- 
sarily any  serious  loss  of  head.  The  size  of  the  throat 
A  with  reference  to  the  normal  size  of  the  pipe  is  governed 
by  the  minimum  quantity  of  water  that  it  is  designed  to 
measure.  Where  this  is  as  low  as  the  sixteenth  or  twentieth 
of  the  normal  flow,  the  throat  must  be  so  small  that  a  serious 
loss  of  head  occurs  in  passing  the  normal  flow.  In  applying 
the  meter  to  water-wheels  this  objection  has  little  force  because 
it  is  not  necessary,  in  that  case,  to  measure  quantities  less  than 
the  fifth  part  of  the  normal  flow.  A  water-wheel  which  gives 
its  best  efficiency  on  a  discharge  of  175  cubic  feet  per  second 
would  never  need  to  draw  less  than  35  cubic  feet.  When  this 
quantity  cannot  be  obtained  it  is  always  better  to  stop  the 


THE    VENTURI  METER.  513 

wheel  and  let  the  water  accumulate.  This  method  can  be 
introduced  into  an  ordinary  manufacturing  establishment  with 
little  disturbance  of  existing  arrangements  and  at  moderate 
expense.  Where  water  is  conveyed  from  the  canal  to  the 
wheels  in  an  iron  pipe,  a  lining  of  timber  can  be  introduced 
into  the  latter  to  contract  the  diameter  and  transform  it  into  a 
Venturi  meter.  The  same  method  can  be  adopted  where  the 
channel  is  a  wooden  penstock  either  round  or  square,  and 
where  exact  methods  are  used  in  measuring  the  change  of 
head  the  latter  need  not  be  great  enough  to  occasion  any 
appreciable  loss. 


CHAPTER    XXIV. 
STORAGE   AND   PONDAGE   OF   WATER. 

THE  total  annual  flow  of  a  stream  in  Massachusetts  is  dis- 
tributed throughout  the  several  months,  taking  the  average  of 
a  series  of  years,  in  about  the  manner  stated  on  page  4. 

This  ratio  of  distribution  is  modified  to  some  extent  in 
other  parts  of  New  England,  the  time  of  extreme  high  and 
extreme  low  water  being  later  in  the  northern  part  and  earlier 
in  the  southern. 

This  statement  exhibits  in  a  very  strong  light  the  chief 
defect  of  water-power,  viz.,  its  extreme  variability.  An 
establishment  depending  wholly  on  water-power,  which  would 
run  its  machinery  throughout  the  year  without  serious  interrup- 
tions, cannot  use  more  than  2  per  cent  of  the  annual  flow  of 
the  stream  in  any  one  month,  or  more  than  24  per  cent  in  a 
year.  Even  with  this  use  of  water  it  would  be  exposed  to 
more  serious  interruptions  than  appear  above.  In  the  months 
of  August  and  September  the  flow  would  naturally  be  below 
the  average  half  the  time,  and  often  below  2  per  cent.  In 
June  and  October  also,  though  the  flow  is  4  or  5  upon  an 
average,  there  would  be  many  days  on  which  it  would  be 
below  3  and  even  below  2.  Moreover,  the  above  statement 
represents  the  average  of  a  long  series  of  years.  In  such  a 
series  years  will  occur  with  a  total  flow  of  not  more  than  half 
the  average,  and  others  with  nearly  or  quite  double.  Several 
years  will  occur  in  succession  falling  25  to  50  per  cent  below 
the  average;  others,  as  much  above. 

It  results  from  these  conditions  that  no  rational  use  can  be 

514 


STEAM-POWER  AND   RESEVOIRS.  $1$ 

made  of  water-power,  subject  to  the  requirements  of  modern 
industry,  without  either  steam-power  to  supply  deficiencies  in 
dry  seasons,  or  storage-reservoirs  to  hold  back  the  surplus  of 
the  high-water  period  for  use  in  time  of  scarcity.  With  reser- 
voirs it  is  possible,  though  hardly  ever  practicable,  to  make  use 
of  the  entire  flow  of  the  stream,  reducing  it  to  a  uniform  average 
stage  throughout  the  entire  year  or  even  for  a  series  of  years, 
or  what  may  be  called  a  cycle  of  years,  that  is,  for  a  period 
long  enough  to  embrace  all  possible  fluctuations  of  the  flow. 
With  the  aid  of  steam-power  alone  it  is  never  possible  to  make 
use  of  the  entire  flow  of  the  stream.  This  would  imply  the 
establishment  of  wheels  and  other  appliances  of  water-power 
to  the  extent  of  the  maximum  flow  of  the  stream,  a  proceeding 
obviously  irrational.  It  is  not  worth  while  to  install  such  plant 
to  a  greater  extent  than  can  be  kept  in  operation  for  three  or 
four  months  in  an  average  year.  This  necessarily  leaves  large 
volumes  of  water  to  run  to  waste,  so  that  the  use  of  steam- 
power  does  not  preclude  the  profitable  use  of  reservoirs. 

In  tables  which  follow,  the  writer  has  endeavored  to  com- 
pute the  values  of  reservoirs  used  in  connection  with  steam,  the 
several  elements  of  the  computation  being : 

First. — The  quantity  of  water  to  be  expected,  month  by 
month  and  year  by  year,  from  a  given  extent  of  drainage- 
ground. 

Second. — The  quantity  of  steam-power  required  to  make  up 
the  deficiencies  of  the  water-power  and  maintain  a  constant 
total  of  power. 

77//>^.— The  change  in  the  relative  proportions  of  water 
and  steam  consequent  upon  reservoirs  of  different  sizes. 

Fourth. — The  cost  of  steam-power. 

The  saving  in  steam-power  resulting  from  reservoirs  deter- 
mines the  amount  of  money  that  can  be  judiciously  applied  to 
their  construction. 

The  flow  of  water  from  a  drainage-area  of  known  extent 
has  been  observed  and  recorded  regularly  by  the  engineers  of 
the  Boston  Water-works  for  nearly  forty  years  past.  Of  these 


5l6  STORAGE  AND    PONDAGE   OF   WATER. 

records,  those  of  the  last  twenty-five  years,  relating  to  the 
Sudbury  River  drainage-area,  a  district  of  75  square  miles,  are 
selected  as  being  most  reliable.  It  is  assumed  that  twenty-five 
years  covers  all  possible  variations  of  flow,  and  that  these 
results  can  be  applied  without  serious  risk  of  error  to  all  parts 
of  New  England  and,  mutatis  mutandis,  to  other  regions  of 
the  United  States. 

Assume  an  establishment  on  a  stream  of  500  square  miles 
drainage-area,  with  a  fall  of  1 5  feet,  and  a  requirement  of  i  ooo 
horse-power,  being  furnished  to  that  extent,  both  with  water- 
wheels  and  steam-engines.  To  avoid  the  complication  of 
pondage,  that  is,  the  holding  back  of  the  flow  during  one  part 
of  the  day  for  use  during  another,  assume  the  use  of  water  to 
be  continuous  during  the  24  hours.  On  a  fall  of  15  feet  1000 
h.p.  requires  about  800  cubic  feet  per  second.  In  computing 
the  expenditure  of  water  we  count  only  the  working-days, 
deducting  the  Sundays,  and  a  holiday  each  from  the  months 
of  February,  April,  May,  July,  September,  November,  and 
December.  So  that  we  have  months  of 

27  days  requiring  1866  millions  of  cubic  feet; 

26      "  "         1797          "  "         " 

25      "  "         1728 

24     "  "         1659 

23      "  "         1590          "  "         " 

Table  17  exhibits  the  flow  of  water  in  the  natural  condition 
of  the  stream,  being  the  monthly  average  in  cubic  feet  per 
second  for  the  entire  period  of  twenty-five  years. 

Table  18  gives  the  aggregate  volume  of  water  furnished 
each  month  in  millions  of  cubic  feet. 

These  two  tables  show  in  a  marked  manner  the  enormous 
fluctuations  of  the  stream.  The  month  of  March,  1877,  fur- 
nished 9973  million  cubic  feet,  September  only  119  million; 
the  former  being  3723  cubic  feet  per  second,  the  latter  only 
46.  During  March,  assuming  the  flow  to  be  uniform,  thirty 
48-inch  wheels  of  the  Rodney-Hunt  pattern  could  have  run  at 
full  gate.  In  September  a  single  wheel  could  hardly  have  run 


COS  T  OF  S  TEA  M-PO  WER.  5  1 7 

at  half  gate.  Other  equally  striking  variations  appear.  Thus, 
in  1887,  the  highest  monthly  average  exceeds  the  lowest 
twenty-six  times;  in  1889  only  a  little  over  four  times. 

Table  19  gives  the  aggregate  steam-power  required  each 
month  to  supplement  the  water-power  and  make  up  a  constant 
total  of  1000  h.p.  The  figures  represent  horse-powers  24 
hours  a  day  throughout  the  month. 

Table  20  shows  the  effect  of  reservoirs  of  different  sizes 
upon  the  quantity  of  water  available  for  power.  It  shows,  in 
millions  of  cubic  feet,  the  volumes  of  water  drawn  from  the 
reservoir,  used  and  wasted,  during  the  month,  and  that  remain- 
ing in  the  reservoir  at  the  close  of  the  month,  for  reservoirs  of 
3000,  5000,  and  10  ooo  millions  of  cubic  feet  respectively. 
-  This  table  runs  through  the  whole  period  of  twenty-five  years 
month  by  month,  and  is  necessarily  voluminous. 

Tables  21,  22,  and  23  show,  month  by  month,  the  steam- 
power  required  with  reservoirs  of  3000,  5000,  and  IOOOO 
million  cubic  feet  respectively,  expressed  in  Table  19  for  the 
case  of  no  reservoirs. 

Table  24  is  a  summary  of  the  whole  matter,  being  the  cost 
of  the  steam-power  each  year.  The  first  column  contains  the 
year;  the  second,  the  cost  of  steam-power  in  the  natural  con- 
dition of  the  stream;  the  third,  the  cost  with  reservoirs  of  3000 
million  cubic  feet;  the  fourth,  with  5000;  the  fifth,  with  10000. 

Cost  of  Steam-power. — The  leading  item  in  the  cost  of 
steam-power  is  coal ;  the  other  items  are  attendance,  lubricants, 
water  for  feed  and  condensation,  repairs,  waste,  and  miscel- 
laneous small  items.  It  is  an  approximately  correct  statement 
that  the  cost  of  coal  is  about  half  the  running  cost  of  the  power. 
Where  the  constant  aim  of  the  steam-user  is  to  keep  down  the 
consumption  of  coal  by  maintaining  the  engine  and  appurte- 
nances in  the  highest  state  of  efficiency  he  will  diminish  the 
cost  of  coal  and  increase  all  the  other  items,  and  the  latter  will 
be  much  the  larger  half.  On  the  other  hand,  when  little 
attention  is  given  to  economy  of  coal,  the  coal  bill  will  be  the 
larger  half  of  the  cost.  The  consumption  of  coal  therefore  is 


5l8  STORAGE  AND    PONDAGE   OF   WATER. 

a  very  variable  factor.  On  trial  runs  of  engines  made  by 
makers  in  fulfilment  of  guarantees,  a  rate  as  low  as  i .  5  pounds 
per  h.p.  hour  and  even  less  is  often  shown,  but  it  is  probable 
that  the  constant  running  of  an  engine  at  this  rate  would 
involve  expense  for  attendance  and  refinements  of  practice 
more  than  offsetting  the  saving  in  coal. 

In  the  trial  of  a  case  of  a  large  number  of  mill-owners 
against  the  city  of  Worcester,  Mass.,  in  1898,  on  account  of 
diversions  of  water  from  Blackstone  River,  it  was  shown  that 
the  several  engines  in  practical  running  consumed  coal  at  the 
rate  of  1.78  to  5.26  pounds  per  h.p.  hour. 

At  the  convention  of  the  United  States  National  Electric 
Light  Association  for  1895,  the  average  consumption  of  ten 
stations,  producing  over  5000  kilowatts  per  diem,  was  stated 
at  5  pounds  per  indicated  horse-power  per  hour.  These 
engines  run  under  conditions  unfavorable  to  economy  on 
account  of  the  great  variation  of  load  from  hour  to  hour. 

A  mill-engine  running  to  supplement  water-power  works 
under  conditions  unfavorable  to  economy.  It  starts  as  soon 
as  the  water-power  falls  below  the  requirements  of  the  mill,  in 
which  case  a  5OO-h.p.  engine  may  run  to  furnish  50  h.p.,  which 
would  cost  per  h.p.  twice  or  three  times  as  much  as  when 
working  at  full  load.  The  same  condition  recurs  toward  the 
end  of  the  dry  season,  when  the  water-power  is  but  little  short 
of  the  mill's  requirements.  The  cost  of  power  in  such  engines 
is  difficult  to  obtain,  for,  though  the  running  expenses  are 
shown  by  the  mill's  records,  the  power  developed  by  the 
engine,  varying  from  day  to  day,  is  not  usually  obtainable.  No 
mill-engine  works  permanently  under  the  most  favorable  con- 
ditions. It  is  the  inevitable  tendency  in  all  mills  to  expand. 
When  the  engine  is  new  it  has  usually  a  capacity  considerably 
in  excess  of  requirements,  and  works  with  too  light  a  load  for 
full  economy.  In  its  later  history,  requirements  increase,  the 
engine  works  under  excessive  load,  with  diminished  expansion 
and  poor  economy. 

Pumping-engines  which  work  into  a  service-reservoir  act 


COST  OF  STEAM-POWER. 


5'9 


under  conditions  favorable  to  economy,  usually  working  at  full 
load  while  working  at  all.  The  records  of  such  engines  usually 
include  the  performance  as  well  as  the  expenses. 

Five  cents  per  million  gallons  raised  i  foot  is  a  rather  low 
cost  of  pumping.  This  is  at  the  rate  of  1.2  cents  per  h.p. 
hour. 

The  average  cost  in  Boston  from  1884  to  1892  was  at  the 
rate  of  6.06  cents  per  million  gallons  raised  I  foot.  This,  if 
we  make  the  common  allowance  of  5  per  cent  for  the  ' '  slip  ' ' 
of  the  pumps,  would  be  at  the  rate  of  1.51  cents  per  h.p.  hour. 
At  the  Edison  Electric-light  Works,  Boston,  in  1895,  the 
running  cost  of  power  was  at  the  rate  of  1.40  cents  per  h.p. 
hour. 

TABLE    17.— FLOW    IN    CUBIC    FEET    PER    SECOND    FROM    500 
SQUARE      MILES     OF      NEW     ENGLAND     DRAINAGE-AREA. 
Average  for  Each  Month. 


Year. 

Jan. 

Feb. 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

I8?5 

80 

"75 

1241 

2358 

919 

672 

248 

305 

160 

499 

1079 

451 

1876 

497 

1058 

3431 

2547 

881 

171 

141 

313 

142 

181 

841 

351 

1877 

508 

734 

3723 

1851 

1074 

462 

156 

93 

46 

488 

1096 

997 

1878 

1400 

1907 

2713 

1258 

1078 

391 

99 

367 

124 

399 

1306 

2458 

1879 

506 

1323 

1802 

2410 

861 

319 

122 

305 

109 

54 

159 

358 

1880 

867  1382 

1060 

904 

397 

136 

I36 

92 

62 

78 

158 

135 

1881 

320  1224 

3097 

1196 

746 

1035 

214 

114 

152 

143 

305 

600 

1882 

959 

1859 

2196 

670 

1000 

409 

67 

43 

237 

231 

167 

243 

1883 

259 

799 

1246 

1044 

725 

232 

89 

607 

70 

143 

158 

149 

1884 

770 

2198 

2928 

2222 

797 

322 

173 

198 

34 

64 

135 

715 

1885 

955 

1047 

1216 

1404 

1033 

329 

48 

1  86 

93 

259 

911 

908 

1886 

1131 

3713 

1592 

I5O6 

557 

157 

89 

73 

9i 

112 

520 

789 

1887 

2003 

2187 

2219 

2026 

789 

320 

88 

165 

85 

147 

285 

497 

1888 

8i3 

1509 

2504 

2046 

1263 

326 

93 

293 

893 

1546 

2133 

2354 

1889 

2152 

925 

1010 

logo 

680 

505 

490 

1107 

637 

951 

1501 

1733 

1890 

970 

1182 

2818 

1450 

1057 

438 

.83 

102 

354 

1757 

940 

770 

1891 
1892 

2334  2696 
1446   716 

3445 
1512 

1816 
674 

440 

973 

320 

33i 

"5 
165 

125 

217 

157 
177 

162 

97 

235 
544 

421 

375 

1893 

335|  H93 

2510 

1644 

2230 

340 

122 

140 

83 

171 

246 

616 

1894 
jSgs 

536   766 
800   418 

1731 

1864 

1269 
1946 

649 
492 

324 
134 

124 

I78 

162 
177 

"5 
69 

289 
1067 

646 
2148 

554 
1378 

1896 

838 

2070 

2966 

1156 

278 

308 

73 

44 

300 

458 

510 

308 

1897" 
1898 

653 
1267 

825 
2338 

1984 
2014 

1172 
1415 

708 
963 

744 
410 

509 
178 

457 
856 

141 

285 

72 
89? 

703 
1536 

1225 
i39i 

1899 

1720 

1068 

3253 

1950 

395 

51 

15 

-27 

72 

89 

237 

170 

Av. 

965 

1408 

2243 

1561 

839 

367 

153 

261 

187 

414 

740 

798 

520 


STORAGE  AND    PONDAGE   OF   WATER. 


During  April,  1896,  the  street-railway  system  of  Boston 
was  obtaining  its  power  at  a  running  cost  of  1.20  cents  per 
h.p.  hour.  These  companies  obtain  coal  at  less  than  $3  per 
U.  S.  ton.  Where  coal  is  subject  to  a  long  railway  haul  and 
at  points  not  accessible  to  railroads  the  cost  must  be  consider- 
ably higher. 

TABLE  18.— FLOW  FROM  500  SQUARE  MILES  OF  NEW  ENGLAND 

DRAINAGE-AREA. 
Aggregate  for  Each  Month,  in  Millions  of  Cubic  Feet. 


Year. 

Jan. 

Feb. 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1375 

213 

2800 

3324 

6113 

2461 

1743 

665 

82O 

416 

1338 

26ll|  1209 

1876 

1332 

2651 

9189'  6602  2359 

445 

378 

840 

369   484 

2lSl    Q-9 

1877 

1363 

1776 

9973  4799  2883;  1197 

418 

251 

119  1309  2842  2671 

1878 

3749 

4614 

7267  3260'  2889  1014 

266 

985 

322  1070  3394  6583 

1879 

1451 

32OI 

4827  6248]  2308 

828 

326 

819 

282   146 

412  958 

1880 

2323 

3464 

2847  2343  1065 

352 

366 

246 

l6o!   2IO 

411 

362 

1881 

859 

2893 

8296 

3100]  1099 

2682 

572 

306 

395   384!  792 

1606 

1882 

2570 

4497  5882 

1738  2676  1060 

179 

"5 

614   619 

420;  651 

1883 

693 

1933  3337 

2706 

1943 

601 

239 

1626 

182 

384 

411;  400 

1884 

2062 

5508 

7843 

5721  2135 

835 

463 

532 

88 

172 

351  1916 

1885 

2559 

2533 

3258 

3639 

2768 

854 

129 

498 

243 

696  2361  2342 

1886 

3027 

8984 

-4265 

3904 

1492 

406 

239 

195 

236 

302  1348  2113 

1887 

5365 

5291 

5942 

5253 

2089 

829 

237 

443 

222 

393 

939 

1332 

1888 

2181 

378i 

6708 

5304 

3382 

845 

243 

786 

23l6|  4142 

5530 

6305 

1.889 

5765 

2237 

2774 

2827 

1822 

1310 

1312 

2966 

1652!  2548  3892 

4643 

1890 

2598 

2861 

7548 

3759 

2831 

1138 

222 

273 

917  4708  2436 

2063 

1891 

6253 

6523 

9227 

4806 

1207 

829 

309 

337 

406   435   611 

1128 

1892 

3874 

1793 

4051 

1747 

2608 

858 

443 

581}  460 

26o|  1398 

1005 

1893 

897 

2886 

6723 

4272 

5973 

891 

327 

375 

215 

458 

648 

1650 

1894 

1436 

1853 

4636 

3289 

1738 

850 

332  434 

298 

774 

1674 

M83 

1895 

2143 

ion 

4993  5044 

1318 

347 

477 

474   179 

2858 

5568 

3691 

1896 

2245 

5186 

7933  2996 

745 

798 

196 

118 

773 

1228 

1322 

1361 

1897 

1749 

1998 

5314  3038 

1896 

1928 

1363 

1224 

365 

193 

1822!  3281 

1898 

3394 

5656 

5394  3668 

2579 

1063 

477 

2293 

739 

2403 

398i 

3724 

1899 

4607 

2582 

8713 

5054 

1058 

132 

40 

-72 

187 

238 

614 

455 

Av. 

2588 

3540 

6011 

4049 

2249 

953 

409 

699 

486 

IIIO 

1919 

2155 

In  the  attempt  to  fix  a  price  which  will  hold  good  for  the 
future,  it  must  be  remembered  that  coal  is  probably  as  low  nou 
as  it  will  ever  be.  The  most  accessible  deposits  of  coal  have 
been  mined;  the  most  favorable  workings  have  been  occupied 
and  in  some  degree  exhausted.  Future  winnings  must  be 
made  at  a  progressively  increasing  expense.  This  condition 


COST  OF  STEAM-POWER. 


$21 


has  been  reached  in  England,  where  the  price  of  coal  has  been- 
advancing  for  several  years  past.  It  is  fully  realized  there  that 
the  supply  of  coal  is  not  inexhaustible,  and  the  same  fact  is 
beginning  to  be  understood  in  this  country. 

TABLE   19.— STEAM-POWER    REQUIRED    TO    MAKE   UP   A    UNI- 
FORM   TOTAL   OF   1000   H.P.  24     HOURS    A    DAY   IN    A   MILL 
COMMANDING     500     SQUARE     MILES     OF     NEW    ENGLAND 
DRAINAGE-AREA,  WITHOUT   RESERVOIRS. 
Head  15  ft.     Power  expressed  in  horse-powers,  24  hours  a  day.     12  cu. 

ft.  per  second  on  i  ft.  fall  taken  as  a  h.p. 


Year. 

Jan. 

Feb. 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

IS75 

1  60 

690 

619 

800 

376 

436 

1876 

786 

824 

609 

823 

774 

561 

1877 

~Ar 

go 

884 

TQ7Q 

876 

84c 

1879 
l88O 

368 

..... 

5O4 

601 

830 

848 
830 

619 

885 

864 
923 

933 
903 

801 
803 

553 
831 

1881 

68 

733 

858 

810 

821 

619 

250- 

1882 
1883 

1884 

670' 

3S 

..... 

I63 

94 

489 
710 

598 

916 

889 
784 

946 
241 

753 

704 
913 

958 

711 

821 
920 

791 
803 
831 

696- 
814. 
106. 

1885 

S«o 

94° 

768 

884 

676 

...... 

1886 

304 

804 

889 

909 

886 

860 

350 

14 

1887 

600 

890 

794 

894 

816 

6,M 

379 

884 

6-u 

' 

•;OQ 

-188 

204 

453 

896 

873 

558 

3& 

450 

600 

856 

844 

804 

798 

706 

474 

1892 

egi 

105 

158 

586 
575 

794 

848 

729 

825 

779 
896 

879 
786 

320 
693 

53i 
230- 

1894 

330 

43 

189 

595 

845 

798 

856 

639 

193 

308- 

1895 
1806 

478 



3*5 
653 

»33 

6TS 

778 
909 

779 
945 

914 

62S 

428 

363 

615 

1807 

115 

7° 

364 

429 

824 

910 

121 

1898 

488 

778 

644 





iSOQ 

506 

936 

981 

1000 

910 

889 

704 

788. 

In  these  computations  we  do  not  deal  with  the  absolute 
cost  of  steam-power,  but  rather  with  the  expense  that  is  saved 
when  water  is  substituted  for  steam  in  an  establishment  pro- 
vided with  both  steam-  and  water-motors;  and,  vice  versa,  the 
expense  incurred  when  water  is  replaced  by  steam.  This  wilB 
of  course  vary  with  the  locality,  but  the  computation  is  made 
on  the  basis  of  I  cent  per  hour  per  horse-power.  When  there 


522 


STORAGE  AND    PONDAGE   OF    WATER. 


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523 


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524  STORAGE  AND    PONDAGE   OF   WATER. 


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EFFECT   OF  RESERVOIRS. 


525 


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S  TO  A' AGE   AND    PONDAGE    OF    WATER. 


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EFFECT   OF  RESERVOIRS. 


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STORAGE   AND    PONDAGE   OF    WATER. 


is  reason  to  think  that  the  cost  should  vary  from  this  figure  the 
results  can  be  modified  accordingly.  We  do  not  here  consider 
the  cost  of  installation  either  of  the  steam-engines  or  the  wheels. 
The  area  occupied  by  the  reservoirs  must  be  regarded  as. 
ineffective,  since  the  evaporation  therefrom  will  be  about  equal 
to  the  rainfall.  It  is  impossible  to  form  any  general  estimate 
of  this  area.  We  must  therefore  regard  the  area  of  the  drain- 
age-ground as  500  square  miles  in  excess  of  that  occupied  by 
the  reservoirs. 

TABLE  21. -STEAM-POWER  REQUIRED  TO  MAKE  UP  A  UNI- 
FORM TOTAL  OF  1000  H.P.  24  HOURS  A  DAY  IN  A  MILL 
COMMANDING  500  SQUARE  MILES  OF  NEW  ENGLAND 
DRAINAGE-AREA. 

With  reservoirs  to  the  extent  of  3000  millions  of  cubic  feet.  Head  15 
feet.  Power  expressed  in  h.p.  24  hours  a  day. 


Year. 

Jan. 

F«, 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

TgTC 

881 

275 

i8~6 

786 

28l 

Q26 

1878 

68 

806 

8-57 

467 

1880 

86^ 

882 

762 

7Q& 

1881 

607 

786 

1  06 

1882 

556 

645 

655 

758 

623 

1883 

845 

794 

762 

769 

1884 

273 

908 

788 

1885 

5°7 

359 

628 

1886 

IO-1 

801 

863 

832 

222 

1887 

473 

872 

782 

457 

258 

1888 

277 

iSSq 

1800 

1&1 

800 

765 

767 

632 

V71 

1802 

1714 

gc6 

191 

442 

428 

876 

74"? 

625 

45 

82O 

cge 

oi 

142 

1895 

IOO 

746 

892 

1896 

324 

934 

550 

342 

2O3 

243 

1897 

542 

1898 

632 

IOOO 

892 

868 

645 

737 

The  anomaly  of  August,    1899,  actually  occurred  on  the 
Sudbury  drainage-basin.      The  flow  fell  short  of  the  evapora- 


STEAM-POWER   REQUIRED    WITH  RESERVOIRS.       533 

tion.  Such  a  result  probably  could  not  occur  on  a  drainage- 
area  of  500  square  miles,  as  such  an  area  could  hardly  fail  to 
embrace  streams  furnishing  considerable  water  in  the  driest 
time. 

In  Table  24,  subtracting  the  average  of  the  third,  fourth, 
and  fifth  columns,  respectively,  from  that  of  the  second,  we 
find: 

The  annual  saving  consequent  upon  a  reservoir 

capacity  of  3000  millions - $13415.92 

The  annual  saving  consequent  upon  a  reservoir 

capacity  of  5000  millions 18  645.41 

The  annual  saving  consequent  upon  a  reservoir 

capacity  of  10  ooo  millions 24  944.96 

TABLE   22.— STEAM-POWER  REQUIRED   TO   MAKE   UP   A 

UNIFORM    TOTAL,  ETC. 
With  reservoirs  to  the  extent  of  5000  millions  of  cubic  feet. 


Year. 

Jan. 

Feb. 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1875 
1876 

88l 

Q5O 

73  1 

39 

299 

1878 

139 

813 

752 

467 

647 

907 

883 

762 

798 

1881 

257 

542 

106 

1882 

87 

656 

757 

6->3 

1883 

, 

841 

794 

762 

769 

1884 

' 

76 

907 

788 

1885 

229 

627 

1886 

734 

832 

220 

225 

781 

457 

2SQ 

1888 
i8«9 
1890 

439 

767 

632 

372 

731 

191 

441 

. 

1  80 

745 

625 

45 

1893 

5OI 

321 

585 

31 

142 

1895 

230 

598 

1896 
1897 
1898 

146 

552 

550 
892 

342 
867 

203 
645 

243 

737 

i»99 

534 


STORAGE  AND    PONDAGE   OF  WATER. 


These  figures  show  what  we  knew  perfectly  well  before, 
viz.,  that  the  benefit  of  reservoirs  to  one  single  establishment, 
or  one  mill  privilege,  is  hardly  ever  sufficient  to  warrant  their 
construction.  The  total  head  to  be  served  must  usually  be  as 
much  as  100  feet  to  bring  such  projects  within  the  range  of 
feasibility.  Exceptions  occur  where  the  level  of  natural  lakes 
can  be  raised  at  slight  expense,  but  with  the  exception  of  the 
northern  part  of  Maine,  such  opportunities  in  New  England 
are  nearly  all  appropriated. 

Suppose  six  such  establishments  lying  consecutively  on  the 
same  stream  with  an  aggregate  fall  of  90  feet.  In  this  case 
the  aggregate  saving  would  be: 

For  a  capacity  of  3000  millions $80  495.52 

•"  "  5000        "       111872.46 

"  "       10  ooo       "      149669.76 

TABLE  23.— STEAM-POWER    REQUIRED    TO   MAKE    UP  A 

UNIFORM    TOTAL,  ETC. 
With  reservoirs  to  the  extent  of  10000  millions  of  cubic  feet. 


Year. 

Jan. 

Feb. 

March 

April. 

May. 

June. 

July. 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1875 
1876 
1877 
1878 
1879 
1880 

881 

8"Q 

88-* 

762 

7o8 

1881 
1882 
1883 

522 

8m 

762 

760 

1884 
1885 
1886 
1887 
1888 
1889 
1890 
1891 

id.8 

1893 
1804 

SOT 

1895 
1896 
1897 
1898 
1800 

190 

COST   Of  STEAM-POWER. 


535 


And  the  cost-  at  which  such  reservoirs  would  be  a  10  per  cent 
investment  would  be : 

For     3000  millions  $804955.20,  or  $268.32  per  million  cu.  ft. 
"      5000          "      i  118724.46,"     223.74   "          "  " 

"    10000          "      1496697.60,"      149.67    "          "  " 

TABLE  24.— COST  OF  STEAM-POWER  TO  MAINTAIN  1000  H.P 
24  HOURS  A  DAY  IN  A  MILL  COMMANDING  500  SQUARE 
MILES  OF  NEW  ENGLAND  DRAINAGE-AREA. 

With  reservoirs  of  different  sizes.  Head  15  ft.  Power  reckoned  at  i  cent 
per  hour  per  h.p. 


Year. 

No  Reservoirs. 

3000  Million 
Cubic  Feet. 

5000  Million 
Cubic  Feet. 

to  ooo  Million 
Cubic  Feet. 

1875 

24841.44 

8  804.64 

5497-44 

5497-44 

1876 

29677.44 

13  703-04 

ii  700.00 

1877 

24292.32 

II  082.24 

3  800.16 

1878 

20304.96 

8118.24 

867.36 

1879 

34862.88 

19  793.28 

12  679.68 

1880 

40616.  16 

28  154.88 

24941.28 

20417.28 

1881 

29  697.  16 

15  993-12 

8  904.48 

3257-28 

1882 

33  795.84 

20  198.88 

13247.52 

1883 

37202.88 

23705-76 

23680.80 

23680.80 

1884 

31  150.08 

18  208.32 

n  051  .04 

1885 

24067.68 

12442.56 

5341-44 

1886 

31  299.84 

18  164.64 

ii  144-64 

1887 

3I393-44 

17  734-68 

10745.28 

1888 

13  172.64 

i  728.48 

1889 

6  932.64 

1890 

I7584-32 

5316.48 

1891 

34  519.68 

20  822.88 

13  790.40 

1892 

30457.44 

15  575-04 

8  505.12 

3675.36 

1393 
1894 
1895 

33908.16 
29927.04 

26  002  .  08 

20  092  .  80 
14071.20 
12030.72 

13079.04 
8  168.16 
4917.12 

3  126.24 
558.00 
i  185.60 

1896 

32  154-72 

16  199.04 

Q  260.  16 

1897 

18  826.08 

3  382.08 

1898 

ii  018.40 

1899 

41805-36 

29  779  76 

23044.32 

5473.72 

Totals  
Averages  .  .. 

690  500.68 
27  620.03 

355  102.76 
14204.11 

224365.44 
8974.62 

66876.72 
2675.07 

At  the  highest  of  these  figures,  opportunities  for  storage 
can  usually  be  found  in  most  New  England  river  valleys ;  at 
the  lowest,  their  occurrence  cannot  usually  be  counted  on.  If 
we  suppose  a  series  of  establishments  on  the  same  stream,  cir- 


53^  STORAGE   AND    PONDAGE    OF    WATER. 

cumstanced  as  above  with  regard  to  power,  having  an  aggre- 
gate fall  of  150  feet — a  case  by  no  means  unusual,  — the  cost 
at  which  reservoirs  would  be  a  10  per  cent  investment  would 
be  $444  per  million  cubic  feet  capacity  for  3000  millions,  $373 
for  5000,  and  $249  for  IOOOO.  It  would  be  rare  indeed  if 
opportunities  for  storage  could  not  be  obtained  at  these  figures. 
Of  course  any  capacity  under  3000  millions  could  be  obtained 
upon  equally  or  more  advantageous  terms.  Many  situations 
exist  in  which  reservoirs  command  a  much  greater  fall  than 
here  assumed.  Certain  reservoirs  on  the  headwaters  of  the 
Blackstone  River,  appropriated  for  domestic  water-supply  by 
the  city  of  Worcester,  Mass.,  in  1895,  were  available  on  a  total 
head  of  more  than  1000  feet,  nearly  all  of  which  is  utilized  for 
power. 

Value  of  Reservoirs. — The  saving  consequent  upon  a 
capacity  of  3000  millions,  which  is  at  the  rate  of  6  million  per 
square  mile  of  drainage-area,  is  $4.47  per  annum  per  million 
cubic  feet  of  capacity,  and  this  is  at  the  rate  of  about  30  cents 
per  foot  of  fall.  The  following  statement  is  therefore  approxi- 
mately true :  The  value  of  reservoirs,  to  the  extent  of  6  million 
cubic  feet  capacity  per  square  mile  of  drainage-ground,  is  30 
cents  per  annum  per  million  cubic  feet  of  capacity  on  each  foot 
of  fall.  The  preceding  tables  show  that  the  value  per  unit  of 
capacity  is  greater  as  the  relative  capacity  is  less.  Where  the 
capacity  is  merely  sufficient  to  avoid  working  the  engines  at  a 
very  uneconomical  load  (see  page  518),  the  value  maybe  twice 
or  three  times  the  above  figure. 

These  tables  throw  light  upon  some  controverted  questions 
in  the  subject  of  power.  How  often,  for  instance,  do  we  hear 
it  said  that  water-power  has  had  its  day ;  is  going  out  of  use ; 
is  being  superseded  by  steam,  etc. ! 

The  total  volume  of  water  discharged  by  the  500  square 
miles  of  drainage-ground  in  the  assumed  period  of  twenty-five 
years  is  654  200  millions  of  cubic  feet.  The  quantity  used  for 
power  in  connection  with  steam  is  329,904  million  in  the 
natural  condition  of  the  stream.  A  mill  using  200  cubic  feet 


VALUE.    OF  RESERVOIRS.  53JT 

per  second,  which  is  about  450  millions  per  month,  would,  as 
appears  from  Table  18,  have  been  short  of  water  sixty  or 
seventy  times  during  the  twenty-five-year  period,  and  this 
quantity  is  the  utmost  that  could  have  been  used  by  such  a. 
mill.  The  entire  volume  used  by  such  a  mill  would  have  been 
135000  million  cubic  feet,  against  329904  million  available 
when  used  in  connection  with  steam.  We  are  entitled  to  say, 
therefore,  that,  of  the  total  flow  of  any  stream,  two  or  three 
times  as  much  water  can  be  used  in  connection  with  steam  as 
can  be  used  to  any  rational  purpose  without  it.  So  far  from 
water  being  superseded  or  rivalled  by  stea'm,  it  is  only  in  con- 
nection with  steam  that  it  attains  its  full  development. 

Another  point  may  be  adverted  to  in  this  connection.  It 
is  sometimes  asserted  that  it  is  cheaper  to  use  steam  alone  than 
to  run  steam  in  connection  with  water-power.  Compare  the 
cost  in  a  mill  running  as  assumed  in  these  tables  with  that  in 
a  mill  using  the  same  power  obtained  from  steam  alone.  We 
will  roughly  estimate  the  cost  of  water-power  plant  at  $100 
per  horse-power.  We  have  taken  I  cent  an  hour,  not  as  the 
absolute  cost  of  steam,  but  as  the  excess  of  cost  of  steam  over 
water,  i.e.,  as  the  additional  expense  incident  to  the  substitu- 
tion of  steam  for  water  in  a  mill  provided  with  both  steam-  and 
water-plant.  We  will  suppose  the  absolute  running  cost  of 
steam  to  be  1.2  cents  per  h.p.  hour,  and  that  of  water  0.2 
cent.  We  will  concede  that  in  a  mill  running  wholly  by 
steam  I  cent  per  hour  may  be  taken  as  the  absolute  running 
cost  of  the  power.  For  a  mill  using  water  and  steam  the 
account  stands  thus: 

Cost  of  steam,  20  per  cent  more  than  in  Table  24.  $33  144. 1 6 
Interest  on  cost  of  water-power  plant,  at  5  per  cent  5  ooo.oo 
Sinking-fund  for  its  entire  renewal,  in  thirty  years.  i  413.00 
Running  cost  of  water,  4587997  h-P-  hours  at 

0.002  = 9^75-99 

Total $48733-i5 

The  item  of  running  cost  appears  excessive,  though  con- 


538  STORAGE  AND   PONDAGE   OF   WATER. 

sistent  \vith   our  preceding   calculations.      If  it  is  so,  it  shows 
that  we  have  done  less  than  justice  to  the  value  of  reservoirs. 

For  a  mill  using  steam  alone,  1000  h.p.,  306 
days,  24  hours  a  day  at  I  cent  per  hour $73  440.0x3 

The  cost  for  steam  alone  is  therefore  about  50  per  cent  in 
excess  of  that  for  steam  and  water. 

Value  of  Water-power. — These  tables  also  throw  light  on 
the  question  of  the  absolute  value  of  water-power,  a  subject  on 
which  widely  divergent  opinions  are  expressed.  If  we  can 
correctly  determine  the  cost  of  power  for  an  establishment  such 
as  is  contemplated  when  run  wholly  by  steam  and  again  when 
run  in  connection  with  water-power,  the  difference,  as  it 
appears  to  the  writer,  may  be  accepted  as  the  accurate  value 
of  the  water-power. 

We  have,  as  above,  cost  by  steam  alone $73  440 

Cost  by  steam  and  water   48  73  3 

Value  of  water  per  annum $24  707 

This  sum  is  what  the  mill  could  afford  to  pay  annually  for 
the  water  used  for  power,  and  still  stand  upon  an  equal  footing 
with  an  establishment  run  wholly  by  steam  at  the  same  place. 

The  foregoing  figures  do  not  apply  to  a  mill  engaged  in 
bleaching,  dyeing,  and  similar  operations  requiring  great 
amounts  of  heat. 

General  Considerations  touching  Reservoirs. — The  natural 
conformation  of  the  earth  was  not  adopted  with  any  special 
reference  to  the  construction  of  reservoirs.  The  sites  most 
feasible  for  holding-grounds  are  most  commonly  near  the 
headwaters  of  the  stream,  with  small  area  of  drainage-ground 
appertinent.  Sites  commanding  large  drainage-grounds  are 
generally  situated  in  broad  river  valleys  involving  high  and 
expensive  dams,  covering  valuable  lands,  flooding  centres  of 
population,  necessitating  changes  of  location  in  railroads  and 
highways.  The  damages  incident  to  flowage  are  generally 
the  controlling  factor  in  the  latter  case.  So  far  as  the  cost  of 
the  dam  is  concerned,  though  absolutely  great,  it  is  generally 


GENERAL    CONSIDERATIONS    TOUCHING   RESERVOIRS.   539 

less  per  unit  of  storage  than  in  the  former  case.  Occasionally 
there  are  exceptions  to  this  conformation,  as  is  strikingly  seen 
in  northern  Maine,  on  the  upper  part  of  the  Penobscot  and 
St.  Croix,  where  numerous  lakes  occur  in  the  main  line  of  the 
river.  The  west  branch  of  the  Penobscot,  at  a  point  2  or  3 
hundred  feet  above  the  sea-level,  with 'a  drainage-area  of  some 
1 800  square  miles,  commands  a  series  of  lakes  susceptible  at 
moderate  cost  of  being  converted  into  reservoirs  capable  of 
reducing  the  flow  of  the  stream  to  uniformity,  not  only  for  a 
year,  but  for  a  cycle  of  years. 

The  chief  obstacle  to  the  construction  of  reservoirs  for 
water-power  lies  in  the  fact  that  the  benefit  to  any  single  user 
of  water  is  rarely  sufficient  to  warrant  the  investment.  Their 
construction  presupposes  a  concert  of  action  between  a  number, 
sometimes  a  large  number,  of  separate  concerns,  and  the  adjust- 
ment of  conditions  and  distribution  of  expense  is  generally  a 
fatal  difficulty.  There  will  ordinarily  be  some  willing  to  accept 
the  benefits  of  the  undertaking  but  unwilling  to  share  the 
expense.  This  matter  might  well  be  controlled  by  law,  as  in 
projects  of  drainage,  irrigation,  maintenance  of  levees,  and 
other  cases  in  which  many  people  share  in  the  control  of  the 
same  natural  agency.  As  the  law  now  stands  in  Massa- 
chusetts, cases  of  this  kind  have  occurred:  -A  few  enterprising 
manufacturers  have  constructed  reservoirs  on  the  headwaters 
of  the  stream  for  their  own  benefit.  Manufacturers  further 
down  the  stream,  though  freely  accepting  the  benefits  of  the 
reservoirs,  have  refused  to  assume  any  share  of  the  expense. 
Later  the  reservoirs  have  been  appropriated  by  a  city  for  pur- 
poses of  domestic  water-supply,  with  ample  compensation  to» 
the  owners.  The  manufacturers  further  down  have  sued  and 
recovered  damages  from  the  city  for  the  loss  of  these  benefits 
which  they  had  refused  to  pay  for. 

The  writer  has  long  been  of  the  opinion  that  the  following- 
simple  legal  provision  would  go  far  toward  remedying  existing- 
difficulties  in  the  organization  of  reservoir  projects.  Let  it  be 
enacted  that  whenever  a  reservoir  is  constructed  for  the 


540  STORAGE  A,ND    PONDAGE   OF   WATER. 

purpose  of  holding  flood-waters  which  are  of  no  value  for 
power,  and  discharging  them  in  form  and  manner  to  be  avail- 
able for  power ;  then  whenever  water  is  discharged  from  said 
reservoir,  every  user  of  water  on  the  stream  below  shall  either 
pay  for  the  same  or  permit  an  equal  quantity  to  run  to  waste. 
Noncompliance  by  the  manufacturer  would  be  readily  detected, 
and  no  one  could  deny  the  justice  of  the  law,  which  excludes 
him  from  benefits  that  he  declines  to  pay  for.  The  variations 
of  level  in  the  mill-pond  incident  to  ponding  the  water  need 
not  impair  the  practicability  of  discharging  a  fixed  quantity  of 
water,  since  a  device  for  so  controlling  the  gate  of  an  orifice 
as  to  discharge  a  fixed  quantity  at  all  stages  of  the  head  is 
wholly  within  the  resources  of  mechanical  skill. 

Cost  of  Reservoirs. — The  following  figures  are  given  on 
the  authority  of  Mr.  Geo.  W.  Rafter.* 

A  system  of  reservoirs  on  the  headwaters  of  the  Hudson, 
contemplated  by  the  State  of  New  York  for  compensation  to 
water-power  on  account  of  water  diverted  for  the  use  of  canals, 
surveyed  and  examined  by  Mr.  Rafter,  with  a  total  capacity 
of  41  593  million  cubic  feet,  is  expected,  according  to  that 
gentleman's  estimate,  to  cost  $62.69  Per  million  cubic  feet  of 
storage. 

The  Bear  Valley  Reservoir  in  California,  with  a  capacity 
of  1766  million,  cost  $121.67  per  million. 

The  Bhatgur  Reservoir  in  India,  5510  million  capacity, 
cost  $73.46  per  million. 

"Die  Long  Valley  Reservoir  in  California,  1436  million, 
cost  $50.73  per  million. 

The  Erkuk  Reservoir  in  India,  3315  million,  cost  $91. .83 
per  million. 

The  Sweetwater  Reservoir  in  California,  holding  784 
million,  cost  $938.70  per  million. 

The  Hemet  Valley  Reservoir  in  California,  holding  6111 
million,  cost  $229.16  per  million. 

*  Report  of  the  State  Engineer  and  Surveyor  of  New  York,  1895, 
P  177- 


RELATION  OF  RESERVOIRS    7O   COAL.  541 

The  Periar  Reservoir  in  India,  holding  6970  million,  cost 
$106.75  per  million. 

The  Betwa  Reservoir  in  India,  holding  1603  million,  cost 
$204.25  per  million. 

The  proposed  Genesee  Reservoir,  holding  7700  million, 
is  estimated  to  cost  $311.69  per  million. 

The  system  of  reservoirs  on  the  headwaters  of  the  Missis- 
sippi, constructed  by  the  United  States  for  the  improvement 
of  navigation,  has  a  total  capacity  of  over  90000  millions 
and  cost  less  than  $9  per  million.  This  was  a  case  where  the 
level  of  natural  lakes  was  raised  by  cheap  wooden  dams  and 
the  land  damages  were  very  slight. 

Reservoirs  surveyed  and  planned  by  the  writer  in  Massa- 
chusetts have  usually  shown  a  cost  of  about  $200  per  million. 

Relation  of  Reservoirs  to  Coal.— The  extreme  cheapness 
of  coal,  during  the  last  quarter  of  a  century,  has  predisposed 
manufacturers  in  New  England  to  look  with  slight  favor  upon 
reservoir  projects  as  adjuncts  of  water-power.  To  the  writer's 
mind  these  works  are  destined  hereafter  to  play  a  more  impor- 
tant part  in  manufacturing  than  hitherto.  There  are  two 
agencies  at  work  tending  in  that  direction:  I.  The  diminish- 
ing rate  of  interest,  which  makes  large  permanent  investments 
preferable  to  high  annual  charges.  2.  The  inevitable  exhaus- 
tion, in  the  course  of  time,  of  our  supplies  of  coal.  The  con- 
sumption of  coal  in  the  United  States  doubled  from  1862  to 
1871,  again  from  1871  to  1881,  and  again  from  1881  to  1893, 
amounting  now  (1900)  to  something  over  200  million  U.  S. 
tons  per  annum.  With  these  facts  to  guide  us  we  might  look 
for  a  consumption  of  400  million  about  1915,  800  million  in 
1933,  1600  million  in  1953,  and  by  1960  a  consumption  which 
would  exhaust  500  square  miles  of  average  workable  coal  land 
in  a  single  year.  There  are  probably  some  300000  square 
miles  of  land  in  the  United  States  underlaid  with  coal,  not 
more  than  50  ooo  of  which  is  workable  at  anything  like  the 
existing  price.  Premonitory  symptoms  of  exhaustion  already 
appear  in  the  coal-supply  of  European  countries.  It  is  prob- 


542  STORAGE  AND    PONDAGE   OF    WATER. 

able  that  the  price  of  coal  in  England  has  passed  its  culminat- 
ing point,  and  will  never  again  be  so  low  as  it  has  been. 
Without  looking  forward  to  the  absolute  exhaustion  of  the  coal- 
supply,  these  figures  make  it  evident  that  materially  higher 
prices  of  coal  may  be  expected  within  a  period  not  too  long  to 
enter  into  the  calculations  of  a  corporation  endowed  with  per- 
petual succession,  when,  as  often  happens,  the  ownership 
remains  in  the  same  family  and  it  is  managed  with  some  refer- 
ence to  the  interests  of  posterity.  Moreover,  in  these  days  of 
gigantic  combinations,  the  monopolization  of  all  existing 
workable  coal  lands  by  a  single  concern  is  an  event  entirely 
within  the  range  of  possibility.  However  much  such  an  event 
would  be  against  the  immediate  interests  of  consumers,  it 
would,  on  a  broader  view,  be  in  harmony  with  the  general 
interests  of  mankind,  tending  to  preserve  for  the  use  of  future 
generations  some  part  of  the  bounties  of  nature  so  lavishly 
wasted  by  the  present. 

It  may  be  interesting  to  note  in  this  connection  that  the 
power  derivable  from  the  St.  Lawrence  River  and  its  tribu- 
taries, from  their  sources  to  the  sea,  is  not  far  short  of  that 
obtainable  from  all  the  coal  mined  in  the  United  States. 

Pondage. — Hardly  less  important  than  storage,  or  the 
retention  of  flood-water  for  use  during  times  of  scarcity,  is 
pondage,  or  the  retention  of  the  flow  of  a  stream  during  non- 
working  hours  for  use  during  working  hours. 

To  have  assumed  the  water  used  during  the  working  hours 
of  the  secular  day,  in  the  preceding  computations,  would  have 
introduced  too  large  an  element  of  hypothesis  and  made  the 
matter  too  complex.  This  embarrassment  we  have  avoided 
by  assuming  the  mill  to  run  throughout  the  24  hours.  Flour-, 
lumber-,  and  paper-mills  usually  run  in  this  manner,  and  require 
no  pondage  unless  it  be  to  hold  the  Sunday  flow.  Textile 
mills  more  commonly  run  in  the  daylight  and  during  the  work- 
ing-hours established  by  law  or  custom. 

We  have  taken  the  maximum  limit  of  the  use  of  water  at 
800  cubic  feet  per  second,  which  is  very  nearly  the  average  flow 


PONDAGE.  543 

of  the  stream  for  the  entire  period  considered.  This  is  as  large 
a  use  as  is  ordinarily  made  by  an  establishment  running  24 
hours  a  day,  though  no  doubt  a  still  larger  use  might  in  some 
cases  be  made  with  advantage.  An  establishment  running  10 
hours  a  day  and  designed  to  make  full  use  of  this  volume  of 
water  must  be  organized  upon  an  entirely  different  basis.  All 
its  buildings,  machinery,  boilers,  engines,  water-wheels,  race- 
ways, etc.,  would  require  to  be  on  a  scale  of  magnitude  about 
2^  times  as  great,  and  it  would  require  pondage  to  hold  800 
cubic  feet  per  second  during  the  time  that  the  wheels  are  not 
running,  viz.,  50400  seconds  each  day;  that  is  to  say,  some- 
thing over  40  million  cubic  feet  of  pondage.  The  maximum 
limit  of  the  use  of  water  would  be  800  X  24  -=-  10  =  1920  cubic 
feet  per  second. 

In  the  actual  running  of  mills  it  is  very  seldom  practicable 
to  use  the  water  to  this  extent.  The  pondage  appertinent  to 
a  mill  privilege  depends  usually  upon  the  height  of  its  dam 
and  the  declivity  of  the  bed  of  the  stream  above  the  dam,  and 
has  no  relation  to  the  requirements  for  power.  Practically  the 
mill  makes  use  of  what  pondage  it  has,  and  beyond  this  allows 
the  night  flow  to  run  to  waste.  The  flow  of  Sundays  and 
holidays  would  largely  run  to  waste  even  with  the  above 
pondage  of  40  millions.  To  avoid  any  waste  of  this  flow,  we 
should  have  to  hold  the  .flow  for  about  40  hours,  requiring  a 
pondage  of  800  X  40  X  3600  =  1 1 5  200  ooo  cubic  feet. 

To  exhibit  the  value  of  pondage  by  the  same  rigorously 
exact  methods  as  have  been  adopted  with  reference  to  storage, 
Tables  25  and  26  have  been  computed,  Table  25  being  merely 
auxiliary  to  the  computation  of  2  6.  These  tables  assume  an 
establishment  with  the  same  drainage-area  and  the  same  fall 
as  in  the  former  case,  running  10  hours  a  day  and  stopping 
I  hour  at  noon,  its  maximum  use  of  water  being  1000  cubic 
feet  per  second.  In  Table  25  the  first  column  is  the  natural 
flow  of  the  stream  in  cubic  feet  per  second,  running  from  50  to 
1000  with  intervals  of  25.  The  second  column  gives  the 
quantity  of  water  which  the  mill  is  able  to  use  with  any  given 


544 


STORAGE  AND   PONDAGE    OF    WATER. 


TABLE   25.— VALUE   OF    PONDAGE    TO    A    MILL   COMMANDING 

500   SQUARE    MILES    OF    NEW    ENGLAND    DRAINAGE-AREA. 

Running  10  hours  a  day  and  capable  of   using   1000  cubic  feet  of   water 

per  second.     Head  15  feet. 


, 

2345 

6789 

a 

10  Million  Cubic  Feet  Pondage. 

20  Million  Cubic  Feet  Pondage. 

=  c' 

'iS 

Gain  from  Pondage. 

Cost  per 
Diem  of 

Gain  from  Pondage. 

Cost  per 
Diem  of 

v-s> 

Draft  of 

Steam- 

Draft  of 

Steam- 

h 

Mill  in 
Cubic  Ft. 

power 
Equiva- 

Mill in 
Cubic  Ft. 

power 
Equiva- 

per Sec. 

Cubic  Ft. 

Horse- 

lent to 

per  Sec. 

Cubic  Ft. 

Horse- 

lent to 

ll 

u. 

per  Sec. 

power. 

Gain  from 
Pondage. 

per  Sec. 

power. 

jain  from 
Pondage. 

50 

140 

90 

112 

$11.  2O 

140 

90 

112 

$11.  2O 

75 

2IO 

135 

169 

16.90 

210 

135 

169 

16.90 

100 

265 

165 

2O6 

2O.6O   !         280 

1  80 

225 

22.50 

12f 

319 

144 

242 

24.20            350 

225 

281 

28.  10 

150 

372 

222 

277 

27.76            420 

270 

337 

33-70 

175 

428 

253 

316 

31-60          475 

300 

375 

37-50 

2OO 

483 

283 

354 

35-40 

530 

330 

412 

4I.2O 

225 

525 

300 

375 

37-50 

.    584 

359 

449 

44-90 

250 

553 

303 

379 

37-90 

639 

389 

486 

48.60 

275 

580 

305 

380 

38.00 

693 

418 

522 

52.2O 

300 

608 

308 

385 

38-50 

748 

448 

560 

56.OO 

325 

635 

310 

387 

38-70 

802 

477 

595 

59-50 

350 

663 

313 

391 

39.10 

857 

507 

634 

63.40 

375 

690 

315 

394 

39-40 

gil 

536 

670 

67.00 

400 

718 

318 

397 

39-70 

960      j        560 

700 

7O.OO 

425 

745 

320 

400 

40.00 

995 

570 

712 

71.20 

450 

773 

323 

404 

40.40 

IOOO 

550 

687 

68.70 

475 

800 

325 

406 

40.60 

IOOO 

«25 

656 

65.60 

500 

828 

328 

410 

41.00 

IOOO 

5oo 

625 

62.50 

52* 

856 

'331 

414 

41-40 

IOOO 

475 

594 

59-40 

550 

883 

333 

416 

41.60 

1000           450 

562 

56.20 

575 

911 

336 

420 

42.00 

looo           425 

531 

53-10 

600 

938 

338 

422 

42.20 

1000           400 

500 

50.00 

625 

965 

340 

425 

42.50 

1000           375 

469 

46.90 

650 

993 

343 

429 

42.90 

IOOO 

350 

437 

43-70 

675 

IOOO 

325 

406 

40.60 

1000    :     325 

406 

40.60 

700 

IOOO 

300 

375 

37-50 

1000     ;       300 

375 

37-50 

725 

IOOO 

275 

344 

34-40 

looo           275 

344 

34-40 

750 

IOOO 

250 

312 

31.20 

IOOO 

250 

312 

31.20 

775 

IOOO 

225 

281 

28.10 

IOOO 

225 

281 

28.10 

800 

IOOO 

200 

250 

25.00 

IOOO 

200 

250 

25.00 

825 

IOOO 

175 

219 

21.90 

IOCO 

175 

219 

21.90 

850 

IOOO 

ISO 

187 

18.70 

IOOO 

150 

187 

18.70 

875 

IOOO 

125 

156 

15.60 

IOOO 

125 

156 

15.60 

900 

IOOO 

100 

125 

12.50 

IOOO 

100 

125 

12.50 

925 

IOOO 

75 

94 

9.40 

IOOO 

75 

94 

9.40 

950 

I  GOO 

50 

62 

6.20 

IOOO 

50 

62 

6.20 

975 

IOOO 

25 

31 

3-  10 

.    IOOO 

25 

31 

3-io 

IOOO 

IOOO 

0 

o 

0 

IOOO 

o 

o 

0 

PONDAGE. 


545 


flow  of  the  stream  and  10  million  cubic  feet'  of  pondage. 
Thus,  with  50  cubic  feet  per  second,  the  entire  flow  of  168 
hours  can  be  saved  and  drawn  in  the  60  working  hours,  giving 
a  draft  of  140  cubic  feet  per  second.  The  same  with  a  flow  of 
75  cubic  feet  per  second.  With  a  flow  of  100  cubic,  feet  per 
second  there  is  a  little  wastage  of  the  Sunday  flow.  Above 
214  cubic  feet  per  second  the  Sunday  flow  is  wholly  wasted. 
Above  this  stage  the  computation  is  as  follows,  say  for  a  flow 
of  225  cubic  feet  per  second: 

In  pond  at  starting  of  mill 10  ooo  ooo  cu.  ft. 

i  hour  flow  held  at  noon,  225  X  3600 810000     " 

Pondage  drawn  in  10  hours  or 

36  ooo  seconds  =  300  cu.  ft.  per  sec..  10810  ooocu.  ft. 
Add  natural  flow  of  stream,  225      "          «' 

Total  draft  of  mill  525      "          " 


TABLE  26.— VALUE    OF    PONDAGE   TO    A    MILL    COMMANDING 
500   SQUARE    MILES   OF    NEW    ENGLAND    DRAINAGE-AREA. 

Running   10  hours  a   day  and  capable  of    using    1000  cubic  feet  of  water 
per  second  on  a  head  of  15  feet. 


Saving  in  Steam-power  with 

Saving  in  Steam-power  with 

Year. 

10  Mil.  Cu.  Ft. 

20  Mil.  Cu.  Ft. 

Year. 

10  Mil.  Cu.  Ft. 

•JO  Mil.  Cu.  Ft. 

of  Pondage. 

of  Pondage. 

of  Pondage. 

of  Pondage. 

1875 

$6619.20 

$8776   70 

1888 

$3459-94 

$4486.81 

1876 

6945.00 

92I4-56 

1889 

4535-54 

5/15.74 

1877 

5530.28 

7580.67 

1890 

4024.94 

545I-I9 

1878 

4230.  op 

6636.11 

1891 

6693.30 

9451-68 

1879 

6741.05 

9231.94 

1892 

8091.25 

10  290.28 

1880 

6432.78 

7346.67 

1893 

6590-13 

8557-46 

1881 

6748.62 

8489.39 

1894 

9003.68 

ii  197-83 

1882 

6615.00 

7992.54 

1895 

5433-84 

7084.76 

1883 

7580.56 

8739-64 

1896 

7225.75 

10  212.52 

1884 

6244.65 

7143-49 

1897 

7494.04 

8876.20 

1885 

4374.88 

5447-31 

1898 

3699.62 

5  061.02 

1886 

5489-30 

6614.11 

IS99 

4053-07 

5I97-05 

1887 

6132.66 

7950.17 

Averages. 

5999.60 

7709.83 

546  STORAGE  AND    PONDAGE   OF   WATER. 

The  third  column  gives  the  gain  from  pondage  in  cubic  feet 
per  second;  the  fourth,  the  same  in  h.p.  ;  the  fifth,  the  value 
of  the  equivalent  steam-power,  or,  rather,  the  expense  saved 
where  water  is  substituted  for  steam,  which  we  take  at  I  cent 
per  hour  or  10  cents  per  diem  per  horse-po\ver.  When  the 
draft  reaches  1000  cubic  feet  per  second  the  gain  from  pondage 
begins  to  diminish ;  and  when  the  natural  flow  of  the  stream 
reaches  1000  cubic  feet  per  second  there  is  no  further  gain  from 
pondage.  The  sixth,  seventh,  eighth,  and  ninth  columns  are 
the  same  as  the  second,  third,  fourth,  and  fifth,  except  that  the 
former  refer  to  a  pondage  of  20  million,  the  latter  to  one  of  10. 

Table  26  gives  the  aggregate  value  of  pondage  for  each 
year  of  the  series  for  10  and  20  millions  respectively.  It  is 
computed  from  Tables  25  and  17  with  the  aid  of  the  calendar 
for  the  several  years.  Thus  for  the  year  1875  with  a  pondage 
of  10  millions: 

Value  for  Mo. 
January.  Average  flow  80  cu.'  ft.  per  sec.  Value  of  pondage 

per  diem.   Table    25,    $18.00.       No.    of    working    days    26. 

Value  for  the  month  18  X  26  = $468.00 

May.  Flow  919.  Val.  per  diem  $10.14.  Working  days  25 253.50 

June.  "  672.  "  "  "  40.88.  "  "  26 1062.88 

July.  "  248.  "  "  "  37.89.  "  26 gSS-M 

Aug.  "  305.  38.54.  26 1002.04 

Sept.  "  160.  "  "  "  29.26.  "  25 73150 

Oct.  "  497.  "  "  "  40.98.  "  26 1065.48 

Dec.  "  451.  "  "  "  40.41.  "  26 1050.66 

Value  of  pondage  for  the  year  at  i  cent  per  h.  p.  hour      $6619.20 

If  for  any  reason  it  should  seem  proper  to  take  the  value 
of  power  at  a  higher  or  lower  rate,  this  result  can  be  changed 
accordingly. 

As  shown  by  Table  26,  the  average  result  for  the  entire 
period  of  twenty-five  years  is  $6000  for  a  capacity  of  10 
millions,  and  $7710  for  20  millions.  These  sums  represent 
the  average  annual  benefit  of  the  respective  amounts  of  pondage 
to  an  establishment  running  under  the  conditions  supposed,  as 
compared  with  one  running  under  the  same  conditions  without 
pondage.  These  results  would  appear  larger  if  we  should 


PONDAGE.  547 

assume  a  larger  maximum  use  of  water;  that  is,  if  we  assume 
the  establishment  capable  of  using  1200  or  1500  cubic  feet  of 
water  per  second  instead  of  1000. 

In  the  case  of  a  series  of  mills  running  10  hours  a  day  and 
supplied  by  storage-reservoirs,  it  often  happens  that  the  daily 
discharge  from  the  reservoirs  does  not  reach  the  mills  within 
the  working  hours,  and  more  or  less  pondage  is  necessary  in 
order  to  make  the  discharge  of  the  reservoirs  available  and 
avoid  waste.  No  greater  amount  of  pondage,  however,  is 
necessary  for  this  purpose  than  would  be  required  to  make  an 
equally  complete  use  of  the  flow  of  the  stream  in  its  natural 
condition ;  generally  less. 

The  fall  of  a  stream  is  hardly  ever  uniform  throughout  its 
course,  but  is  often  concentrated  in  a  few  miles  of  rapids  with 
long  reaches  of  quiet  water  above  and  below.  These  rapids 
are  occupied  by  a  succession  of  dams  with  little  opportunity 
for  the  creation  of  pondage.  The  common  interest,  in  that 
case?  calls  for  a  large  pond  at  the  head  of  the  line,  and  each 
mill,  on  starting,  draws  from  its  own  pondage  only  till  it 
receives  water  from  the  next  pond  above,  so  that  the  single 
pond  serves  the  whole  series.  This  pond  may  have  a  value 
many  times  as  great  as  computed  above.  Such  a  case  exists 
at  Gardiner,  Maine,  where  there  is  a  series  of  dams  supplied 
by  the  Cobbosseecontee  River,  which  stream,  draining  about 
21  5  square  miles,  has  some  2500  or  3000  million  cubic  feet  of 
storage  capacity,  and  has  a  pond  at  the  head  of  the  series  of 
dams,  capable  of  holding  the  discharge  of  the  reservoirs  while 
the  mills  are  stopped. 

The  most  fortunate  condition  is  where  the  same  basin 
serves  both  for  storage  and  pondage,  as  occurs  at  Rockville  in 
Connecticut.  Here  Lake  Shenipset,  near  the  head  of  the 
Hockanum  River,  has  a  drainage-area  of  some  15  square 
miles,  and  is  controlled  by  a  dam  to  the  extent  of  some  24 
feet,  holding  practically  the  entire  flow  of  the  drainage-ground. 
Below  the  dam  is  a  series  of  mill  privileges  with  an  aggregate, 
fall  of  more  than  250  feet.  The  declivity  is  so  great  %t 


548  STORAGE  AND    PONDAGE   OF   WATER. 

the  pondage  appurtenant  to  each  dam  is  very  small.  These 
are  mostly  textile  mills  and  run  but  10  hours  a  day.  The 
reservoir-gates  are  opened  only  during  working-hours.  As 
soon  as  any  mill  commences  to  draw  from  its  pond,  the  mill 
above  commences  to  discharge  into  the  same,  and  very  little 
water  runs  to  waste.  Very  rarely  does  so  small  an  extent  of 
drainage-ground  furnish  so  large  an  amount  of  power. 


CHAPTER  XXV. 

COMPUTATION   OF   DAMAGES  TO   MILL-OWNERS   RE- 
SULTING    FROM   THE   DIVERSION   OF   WATER. 

WATER  applied  to  the  generation  of  power  is  a  utility  which 
can  readily  be  replaced  by  steam.  Water  for  drinking,  clean- 
liness, sanitary  and  domestic  uses  is  a  necessity  for  which  no 
substitute  can  be  found.  In  the  growth  of  communities  and 
the  aggregation  of  population  in  great  masses,  the  necessity  is 
constantly  arising  for  the  diversion  of  streams  from  their  natural 
channels  for  purposes  of  domestic  water-supply.  The  State 
readily  grants  such  rights  of  diversion  on  the  ground  that  the 
new  application  of  the  water  is  more  beneficial  to  mankind  than 
the  old ;  but  such  rights,  whether  so  stipulated  in  the  grant  or 
not,  are  always  coupled  with  the  obligation  to  pay  the  damages 
incident  to  the  diversion.  The  estimation  of  these  damages  is 
therefore  a  duty  which  frequently  devolves  upon  the  hydraulic 
engineer. 

The  nature  of  the  mill-owner's  right  in  the  water  is-not  that 
of  ownership.  He  does  not  own  the  water.  The  only  thing 
he  has  a  right  to  is  the  effect  of  the  water  while  passing  from 
the  upper  to  the  lower  level.  He  has  the  right  to  have  the 
water  flow  past  his  mill  and  through  his  wheel,  and  after  it  has 
made  this  journey  he  has  no  further  control  over  it.  His  loss 
is  fully  made  good  by  a  sum  of  money  sufficient,  under  existing 
conditions,  to  supply  in  perpetuity,  the  power  lost  by  his  mill. 
The  theory  of  the  law  is  that  the  loss  is  represented  by  the  dim- 
inution of  market  value,  i.e.,  by  the  difference  in  the  market 
value  of  the  property  before  and  after  the  diversion,  technically 

549 


55°      COMPUTATION   OF  DAMAGES    TO   MILL-OWNERS 

called  the  "  taking,"  of  the  water;  but  the  extreme  clumsiness 
and  inapplicability  of  this  rule  has  led  courts  to  accept  the  cost 
of  replacing  the  lost  power  as  the  diminution  in  market  value. 

The  legislative  grant  of  authority  to  divert  or  "  take  "  the 
water  takes  different  forms.  Sometimes  it  is  a  certain  number 
ot  millions  of  gallons  daily.  Sometimes  it  is  the  right  to  divert 
the  entire  flow  of  a  stream,  that  is,  to  abstract  a  definite  number 
of  square  miles  of  drainage-ground.  Sometimes  it  is  the  right 
to  divert  the  flood-waters  or  a  certain  portion  thereof,  in  which 
case  little  injury  is  done  to  the  water-power  unless  favorable 
opportunities  exist  for  the  storage  of  water. 

In  the  trial  of  such  cases  many  false  and  untenable  claims 
are  set  up  on  either  side.  The  mill-owner  usually  figures  up 
his  claim  in  this  way:  "  You  take  from  me  so  many,  say  25, 
cubic  feet  of  water  per  second.  This,  on  the  existing  fall  of 
15  feet,  and  assuming  an  efficiency  of  80  per  cent  in  my 
wheels,  amounts  to  some  34  h.p.  Power  furnished  to  small 
consumers  commands,  say,  $75  per  annum  per  h.p.,  which 
would  amount  to  $2550  per  annum.  The  sum  which  would 
yield  this  annuity  at  the  highest  attainable  secure  and  perma- 
nent rate  of  interest,  say  3  per  cent,  is  $85  ooo. "  In  addition 
to  this  the  loser  usually  sets  up  a  claim  for  the  installation  of 
additional  steam-power  to  the  extent  of  the  diversion.  The 
taker  reckons  in  this  manner:  "We  concede  that  we  take  25 
cubic  feet  per  second  usable  on  a  fall  of  1 5  feet.  It  is  only  for 
six  month' s  in  the  average  year  that  this  diversion  does  you  any 
injury,  the  remainder  of  the  year  you  have  an  abundance  with- 
out it.  The  efficiency  of  your  wheels,  in  their  ordinary  running, 
cannot  be  placed  higher  than  75  per  cent,  so  that  your  loss  is 
but  31  h.p.  This  loss  subjects  you  to  no  expense  that  you  can 
clearly  define  and  specify  other  than  the  burning  of  some  93 
pounds  of  additional  coal  per  hour,  worth,  say,  2  mills  a  pound 
or  $1.96  per  diem.  This  for  half  a  year  would  amount  to 
$300.  This  annuity  used  in  your  business  would  be  worth 
6  per  cent  to  you  and  should  be  capitalized  on  that  basis. 
Therefore  $5000  is  all  you  are  entitled  to. ' '  With  such  diverg  - 


RESULTING   FROM    THE   DIVERSION   OF    WATER.     55! 

ence  of  views  it  is  not  strange  that  a  mutual  agreement  is 
difficult. 

The  writer  regards  the  following  as  the  equitable  principles 
governing  such  estimates.  The  loser  can,  in  general,  make 
no  claim  for  additional  steam-plant  necessitated  by  the  diver- 
sion. It  is  only  in  virtue  of  his  ability  to  make  a  rational  use 
of  the  water  that  he  suffers  loss  by  the  taking  of  it.  Such 
rational  use  implies  steam-power  sufficient  to  supplement  the 
water-power  at  all  stages  of  the  stream.  Consider  a  mill  using 
1000  h.p.  on  the  stream  of  500  square  miles,  as  already 
assumed,  and  suppose  50  square  miles  to  be  diverted.  The 
total  flow,  shown  by  Table  17,  falls  many  times  below  100,  often 
below  50,  cubic  feet  per  second.  The  engine  should  be  capable 
of  working  with  fair  economy  when  the  stream  is  as  low  as  100 
cubic  feet  per  second.  That  is,  it  should  furnish  875  h.p.  with 
fair  economy.  Such  an  engine  would  yield  1000  h.p.  with 
slightly  diminished  economy  or  slightly  increased  cost  per  h.p. 
After  the  diversion  the  stream  would  yield  90  cubic  feet  per 
second  where  it  now  yields  100,  45  where  it  now  yields  50,  etc. 
The  only  effect  of  the  diversion  is  to  prolong  the  time  during 
which  the  engine  works  with  diminished  economy.  The  diver- 
sion unquestionably  necessitates  increased  steam-power,  but 
nothing  could  be  more  fanciful  than  the  claim  that  it  necessi- 
tates increased  steam-plant.  It  is  to  be  remembered  that  there 
will  be  years  after  the  diversion  with  greater  flow  than  others 
before,  and  years  before  the  diversion  with  less  flow  than  others 
afterwards.  The  existence  of  storage-reservoirs  does  not  alter 
this  conclusion,  because  the  mill-owner,  in  fixing  the  capacity 
of  his  engine  without  any  reference  to  the  diversion,  is  bound 
to  take  notice  that  the  reservoirs  are  liable  to  be  exhausted 
while  the  stream  is  in  its  lowest  stage. 

Still  more  irrational  is  the  claim  that  the  cost  of  supplying 
the  Tost  power  should  be  computed  upon  the  basis  of  an  extra 
steam-plant  of  the  precise  capacity  required  to  supply  the  same, 
which  would  be  vastly  more  expensive  in  operation.  The 
owner  is  entitled  to  reimbursement  of  the  expense  of  repairing 


552      COMPUTAl^ION  OF  DAMAGES    TO   MILL-OWNERS 

the  loss  incident  to  the  diversion.  But  this  loss  must  be 
repaired  in  a  reasonable  manner.  Now,  the  reasonable  mode 
of  meeting  fluctuations  in  the  flow  of  a  stream  is  the  one 
universally  employed,  viz.,  an  engine  of  sufficient  capacity,  and 
whether  these  fluctuations  arise  from  vicissitudes  of  season  or 
from  human  agency  is  immaterial  in  this  connection. 

The  mill-owner  cannot  claim  the  market  value  of  the  power 
producible  from  the  diverted  water,  that  is,  of  power  trans- 
mitted electrically  or  otherwise,  and  placed  at  the  disposal  of 
the  consumer.  The  loser  is  entitled  to  the  market  value  of  the 
thing  lost.  The  loser  of  a  basket  of  eggs  is  entitled  to  the 
market  value  of  the  eggs,  not  to  the  market  value  of  the 
chickens  that  might,  with  trouble  and  labor,  have  been  pro- 
duced from  them.  The  loser  of  water  is  entitled  to  the  market 
value  of  the  water,  in  the  market  that  is  open  to  it.  This 
market  is  the  water-wheel,  and  the  only  value  that  can  be 
obtained  for  the  water  is  a  certain  saving  in  the  cost  of  the 
power.  The  value  of  this  saving  is  what  the  user  is  entitled 
to. 

Wildly  extravagant  claims  are  often  set  up  when  storage- 
reservoirs  are  taken  by  municipalities.  It  is  contended  that 
these  have  a  great  value  by  reason  of  their  adaptability  to  pur- 
poses of  water-supply;  that  they  are  indispensable  and  would 
command  a  high  price  for  that  purpose,  etc.  In  the  taking  of 
Whitehall  Pond  by  the  city  of  Boston,  several  years  ago,  an 
unheard-of  award  was  made  on  this  ground.  Municipalities 
are  entrusted  by  the  State  with  the  power  of  seizure  and  con- 
demnation. Without  this  power  municipal  development  might 
be  wholly  arrested  by  the  cupidity  of  individual  landowners. 
The  price  paid  for  property  taken  is  what  the  property  is  worth 
to  the  owner,  not  what  it  is  worth  to  the  taker.  The  value 
of  a  cup  of  water  to  the  owner  of  a  spring  is  trifling,  not  worth 
taking  account  of.  To  the  wayfarer  perishing  with  thirst  it 
may  be  of  such  value  that  he  would  give  all  his  wealth  rather 
than  not  have  it.  To  say  that  a  town  having  the  right  of  seizure 
and  condemnation  ought  to  pay  for  a  reservoir  or  other 


RESULTING  FROM   THE  DIVERSION  OF   WATER.     553 

adjunct  of  water-power  the  same  price  that  it  might  be  com- 
pelled to  pay  if  it  did  not  have  that  power,  is  simply  an  attempt 
to  evade  the  legal  maxim  that  the  value  of  the  thing  taken 
cannot  be  regarded  as  enhanced  by  the  taking.  The  value  of 
the  reservoir  must  be  determined  by  the  use  which  the  owner 
can  make  of  it  for  his  own  purposes. 

On  the  other  hand,  the  theory  sometimes  set  up  by  muni- 
cipalities that  the  value  of  the  power  diverted  is  measured  by 
the  cost  of  coal  required  to  replace  it  is  untenable.  It  is  true 
that  it  is  difficult  precisely  to  define  and  specify  the  other 
elements  of  cost.  Nevertheless  we  know  that  the  entire  cost 
of  steam-power  is  ordinarily  something  like  double  the  cost  of 
the  coal  consumed,  and  that  if  the  entire  power  were  taken  it 
would  have  to  be  paid  for  upon  that  basis  or  something  like  it. 
To  say  that  a  mill-owner  ought  to  dispose  of  a  small  part  of 
his  power  at  a  lower  rate  than  he  would  be  entitled  to  if  he 
sold  the  whole  of  it  is  certainly  an  unfair  proposition.  The 
reverse  statement  would  be  more  equitable,  viz.,  a  small  part 
of  the  power  should  command  a  higher  rate  per  h.p.  than  the 
whole. 

In  such  cases  some  application  can  be  given  to  the  propo- 
sition that  doubtful  points  should  be  construed  in  the  claimant's 
favor.  He  does  not  seek  to  sell  his  power.  It  is  taken  from 
him,  presumably  without  his  consent.  He  must  be  fully  paid  for 
it.  The  sufficiency  of  the  payment  must  not  be  open  to  doubt. 
He  must  not  be  subjected  to  loss  or  to  serious  risk  of  loss  in 
the  transaction.  This  requires  that  points  of  uncertainty  and 
doubt  should  be  construed  in  his  favor.  A  different  principle 
must  be  adopted  in  estimating  the  value  of  a  water-power  for 
the  guidance  of  an  investor.  Here,  the  estimate  must  not  leave 
any  doubt  as  to  the  value  assigned  the  property.  It  must  not 
subject  the  investor  to  loss  or  serious  risk  of  loss.  Doubtful 
elements  of  value  must  be  excluded,  and  doubts  must  be  con- 
strued against  the  property.  For  an  engineer,  therefore,  to 
estimate  the  value  of  water  rights  at  a  higher  figure  when 


554      COMPUTATION  OF  DAMAGES    TO   MILL-OWNERS 

acting  on  behalf  of  a  claimant  than  on  behalf  of  an  investor 
is  not  necessarily  inconsistent  with  good  conscience. 

The  tables,  under  the  head  of  Storage  and  Pondage,  suggest 
the  method  to  be  adopted  for  computing  the  value  of  a  given 
water-power,  but  they  can  be  more  specific  when  applied  to  a 
specific  case.  The  elements  of  the  computation  are:  (i)  The 
drainage,  and  (2)  the  flow  per  square  mile  to  be  expected  for  a 
series  of  years.  From  these  we  find  (3)  a  table  of  the  quantity 
of  water  to  be  expected  from  the  entire  drainage-ground  for  a 
series  of  years,  Table  17.  (4)  The  fall,  which  we  have 
assumed  at  1 5  feet,  but  in  fact  it  will  vary  from  day  to  day 
according  to  the  stage  of  the  stream.  (5)  The  pondage, 
whether  directly  appertinent  to  the  dam  or  derived  from  ponds 
higher  up  the  stream.  (6)  The  largest  flow  of  the  stream  that 
it  would  be  judicious  to  provide  for  the  use  of.  This  is  usually 
taken  as  about  the  average  of  the  fourth  highest  month,  being 
965  cubic  feet  per  second  in  Table  17,  excluding  pondage. 

We  would  now  proceed  to  form  a  table  of  averages  running 
through  the  entire  series  of  years,  generally  month  by  month. 
This  would  contain: 

1.  The  flow  of  the  stream. 

2.  The  quantity  of  water  added  to  the  natural  flow,  during 

working-hours,  by  pondage.  This  may  require  more 
than  one  column,  as  there  may  be  more  than  one 
pond. 

3.  The  quantity  of  water  susceptible  of  use  by  the  mill. 

4.  The   head   acting   on   the    wheels.      This    may  require 

several  columns,  as  there  are  several  sources  of  loss 
of  head,  viz.,  in  head-race;  in  tail-race;  in  wheel- 
pits  and  penstocks.  These  losses  must  be  determined 
by  observation  coupled  with  the  mechanical  principle 
that  either  of  these  losses  is  proportional  to  the 
square  of  the  velocity. 

5.  The  power.      This  is  most  conveniently  expressed    in 

horse-power  hours,  the  unit  being  a  horse-power  for 
one  hour. 


RESULTING   FROM   THE  DIVERSION  OF  WATER.      555 

6.  The  value  of  the  power  per  diem. 

7.  The  number  of  working-days  in  the  month. 

8.  The  value  of  the  power  for  the  month. 

9.  The  value  of  the  power  for  the  year. 

The  average  of  the  quantities  in  the  ninth  column,  for  the 
series  of  years,  must  be  taken  as  the  true  value  of  the  power 
which  the  entire  drainage-ground  is  capable  of  yielding  esti- 
mated with  reference  to  the  given  fall. 

Assuming  a  case  of  diversion  of  a  certain  part  of  the  drain- 
age-area, 50,  60,  etc.,  square  miles,  we  form  a  new  table 
embracing  the  remaining  area,  and  compute  the  value  of  power 
on  the  diminished  area  in  the  same  manner.  The  difference 
between  these  two  results  would  be  the  value  of  the  power  lost 
if  the  mill  were  in  a  position  to  use  the  assumed  quantity  of 
water.  Generally,  however,  the  existing  use  of  water  is  much 
less  than  the  maximum  on  which  these  results  are  based.  The 
power  available  but  not  in  use  cannot  be  accounted  valueless, 
"but  it  is  of  less  value  than  that  already  in  use.  We  now  find 
the  maximum  power  in  present  use  by  the  mill,  and  go  over, 
the  tables  and  separate  the  power  into  two  parts:  (i)  the 
power  actually  in  use;  (2)  the  power  not  now  in  use  but 
available  at  a. later  date.  The  history  of  the  mill  and  the 
growth  and  expansion  of  the  manufacuture  will  show  the 
average  date  at  which  it  will  have  use  for  the  entire  power. 
The  value  of  the  power  in  the  second  category  may  be  regarded 
as  a  sum  of  money  due  at  that  later  date,  and  subject  to  a 
corresponding  discount.  Making  this  discount  and  adding  the 
sums,  we  have  the  true  value  of  the  water-power  before  and 
after  diversion.  The  difference  is  the  annual  value  of  the  loss 
sustained  by  the  owner,  and  he  should  receive  a  sum  of  money 
sufficient  to  yield  this  annuity  at  such  rate  of  interest  as  can 
be  obtained  on  safe  and  permanent  investment. 

It  would  appear  at  first  view  that  instead  of  forming  a  table 
running  through  a  series  of  twenty-five  years  we  might  take  the 
average  of  the  several  months  in  Table  1 7  and  thus  form  an 
ideal  year  to  serve  as  the  basis  of  our  computations.  The 


556      COMPUTATION   OF  DAMAGES    TO  MILL-OWNERS 

objection  to  this  method  is  that  it  would  include  a  large 
quantity  of  water  which  actually  runs  to  waste.  Thus  the 
average  of  all  the  Decembers  in  Table  17  is  798  cubic  feet  per 
second,  which,  being  below  the  assumed  maximum  use,  would 
all  be  included  as  usable  water,  whereas  in  point  of  fact  there 
are  no  less  than  six  months  of  the  series  in  which  large  quan- 
tities of  water  ran  to  waste. 

It  would  be  equally  fallacious  to  compute  the  loss  on  the 
assumption  that  the  power  lost  is  in  proportion  to  the  area 
diverted.  In  the  case  we  have  supposed  of  50  square  miles 
diverted  from  a  water-power  commanding  an  area  of  500,  sup- 
pose the  mill  to  have  use  for  water  up  to  the  average  of  the 
seventh  month  in  the  order  of  flow,  i.e.,  to  waste  water  for  five 
months.  There  are  five  months  of  the  year  that  the  diversion 
does  the  mill  no  injury,  and  during  four  of  the  remaining 
months  the  flow  is  very  small.  So  that  the  quantity  of  power 
diverted  from  the  mill  is  in  no  sense  proportional  to  the, 
drainage-area  diverted.  If  we  suppose  a  number  of  successive 
diversions  of  50  square  miles  each,  the  second  would  reduce 
the  period  of  wasting  water.  Each  successive  diversion  would 
cut  more  and  more  into  the  months  of  abundant  flow,  and  each 
would  do  a  greater  injury  to  the  water-power  than  the  one  pre- 
ceding. If  the  drainage-area  were  provided  with  storage- 
reservoirs  to  the  extent  of  impounding  all  the  water,  then  the 
injury  consequent  upon  any  specific  diversion  would  be  propor- 
tional to  the  area  diverted. 

Industries  Requiring  Heat. — A  case  which  occasions  much 
perplexity  is  that  of  mills  carrying  on  the  operations  of  bleach- 
ing, dyeing,  printing,  etc.,  requiring  great  quantities  of  heat.  In 
this  case,  the  steam  from  the  engines,  instead  of  passing  to  the 
condensers  and  so  increasing  the  available  power,  is  led,  under 
a  pressure  of  5  or  6  pounds,  to  the  heating-pipes.  By  sacrific- 
ing the  power  due  to  condensation,  more  than  nine-tenths  of 
all  the  heat  imparted  to  the  steam  may  be  made  available  for 
industrial  purposes.  Establishments  of  this  kind  exist  in  which 
it  makes  but  slight  difference  in  the  consumption  of  coal 


RESULTING   FROM    THE   DIVERSION   OF   WATER.     557 

whether  the  water-wheels  run  or  not,  and  where  a  question  of 
the  value  of  water-power  so  applied  arises,  it  is  contended, 
with  a  show  of  reason,  that  it  is  of  no  value,  since  it  could  be 
dispensed  with  with  but  slight  increase  of  expense — an  increase 
not  exceeding  the  expense  of  maintaining  wheels. 

The  true  view  of  this  case  appears  to  me  this :  Water-power 
is  perpetual ;  the  applications  of  water-power  are  temporary 
and  transient.  The  running  by  water-power  of  an  establish- 
ment which  is  susceptible  of  being  operated  by  a  small  fraction 
of  the  heat  required  in  the  industry  is  not  a  judicious  use  of 
water-power.  But,  like  all  other  property,  water-power  cannot 
be  accounted  valueless  because  owners  are  not  making  a  profit- 
able use  of  it.  Its  value  is  to  be  determined  from  the  uses  of 
which  it  is  susceptible,  not  the  use  to  which  it  is,  for  the  time 
being,  applied. 

Nevertheless  water-power  so  applied  cannot  be  accounted 
of  the  full  value  of  water-power  in  profitable  application, 
because,  although  it  is  susceptible  of  a  profitable  use,  a  certain 
time  must  necessarily  elapse  before  it  can  be  cpnverted  to  that 
use,  and  this  time  during  which  it  must  continue  in  unprofitable 
use  may  properly  be  considered  in  abatement  of  its  value. 


INDEX. 


PAGE 

Accumulator -qg 

Adiabatic  change  of  volume 4^ 

Air,  solution  of,  in  water 4^5 

compressed,  isothermal  change 4™ 

adiabatic  change 4^ 

chamber  on  penstock 46g 

compressor 4Ig 

American  turbine 287 

Applying  water-power 365 

Bear- trap  Dam 133 

Bear  Valley  Dam IC;2 

Bouzey  Dam 215 

Boyden  turbine 266 

discharge  of 271 

Bradfield  Reservoir,  failure  of 205 

Breast-wheel 242 

Bridge-tree 321 

Canals  for  water-power 348 

wasteway  in 225,  365 

ice  in 226 

sluices  for 227 

in  rock   349 

side  slopes 348 

velocity  in 350 

slope  of  bottom 354 

effect  of  ice-sheet  in 356 

lining  or  sheathing 358 

at  Lowell 369 

Holyoke 371 

Lawrence • 374 

Case  of  turbine 306 

Centrifugal  force 262 

559 


50  INDEX. 

PAGE 

Clutch,  friction 326 

Compressed  air 4TI 

motors 420 

raising  liquids  by 421 

power-house 4yo 


installation  at  Paris. 


Offenbach. 


422 

423 

Birmingham 423 

Chapin  Mine 425 

Compressing  air  by  the  direct  action  of  water 426 

Conductor,  electric 432 

Conductivity 436 

Current-meter 488 

acoustic 492 

rating  of 493 

Dam  at  Plainfield,   Conn 81 

on  Bear  River,  Northern  Utah 83 

at  Holyoke  on  the  Connecticut  River 85 

at  Lowell,  Mass 99 

of  Essex  Co.  at  Lawrence 101 

on  Colorado  River  at  Austin,  Tex 105,  217 

new  masonry,  at  Holyoke 106 

on  the  Hudson  at  Mechanicsville,  N.  Y in 

and  bridge  combined  at  Lonsdale,  R.  1 112 

rock-fill,  at  Escondido,  Cal 165 

Otay  Creek,  Cal 167 

on  Pecos  River,  N.  M 171 

Dams  for  water-power 15 

effect  of  flood-height 20 

form  with  reference  to  discharge 26 

with  steps 30 

inclination  of  top 32 

curved  in  cross-section 33 

outline  in  plan 37 

of  timber  and  earth 43 

of  trees 57 

of  logs 62 

in  deep  water 67 

of  sawed  or  hewn  timber  with  earth  or  loose  stone 68 

of  cribwork 74 

with  curved  planking 7.9 

of  masonry 93 

compared  with  dams  of  timber 96 

movable 133 

Poiree  needle 137 


INDEX.  561 

PACK 

Dams,  movable,  Chanoine  wicket  ..................................  I4I 

rock-fill  .....................................  ......'....I'."!:  164 

Damages  for  diversion  of  water  .....................................  540 

Datum  plane  ..............................................  .„_ 

Diffuser  ...................................  .........................  3og 

Discharge  of  Boyden  wheel  ..........  .  .................  ...  .............  2^j 

wasteway  ..............................................  I9g 

Disconnecting  mechanism  ..........................................  2 


Diversion  of  water  from  mill-owners  .......................  .........  549 

Division  of  fall  .....................................................  377 

Draft-tube  ..........................................................  307 

Duplex  wheel  ......................................................  297 

Electric  transmission,  analogy  with  other  methods  ...................  429 

potential  in  ...................................  435 

efficiency  of  ..................................  437 

Lauffen  to  Frankfort  ..........................  438 

Silverton,  Col  ................................  440 

Fresno,  Cal  ...................................  441 

Redlands  to  Los  Angeles  ......................  441 

Embankments  ......................................................   149 

made  by  sluicing  ......................................  172 

Energy,  the  sun  the  source  of  ........................................        I 

storage  of,  by  pumping  .....................................  409 

Escondido  dam  .....................................................    165 

Failures  of  high  dams  ..............................    ..............   204 

Fishways  ........................................................    124 

Flashboards  ........................................................   116 

Floats  ..........................................................  478,  480 

sources  of  error  in  ............................................  485 

Flood  from  breaking  of  reservoir-dam  ...............................  222 

height,  effect  on  dam  .........................................     20 

Floods  as  affected  by  course  of  streams  .............................       3 

Flow  of  streams  ....................................................       2 

measurement  of  .....................................   505 

portion  available  for  power  .....................  515,  536 

data  concerning  ...................................       6 

Flo  wage  occasioned  by  dam  .........................................       8 

Flume  ..............................................................  3" 

Fri-tion-clutch  .....................................................  326 

Gates  .......  .  ......................................................  227 

vertical  ......................  •  ................................  228 

with  counterweight  ............................................  230 

hydraulic  lift  .............................................  228 


52  INDEX. 

PAGE 

Gates,  turning 234 

Gate-houses , 237 

Gauges 497 

Gileppe  dam 190 

Hamiz  dam 192 

Head,  loss  of,  in  pipes 399 

Height  of  water,  measurement  of 496 

Hook-gauge 501 

Hurdy-gurdy  wheel 300 

Hydraulic  ram 426 

Ice,  formation  of 226 

in  canals 356 

at  Lachine  Rapids 455 

Industries  requiring  heat 556 

Interest,  rate  of,  as  related  to  engineering 94 

formulas  for 95 

diagram  for • 96 

Measurement  of  water 478 

Otay  Creek  dam 167 

Pecos  River  dam 171 

Penstock 330 

Pitot  tube 495 

Pondage  of  water 542 

Power-house  on  Low  Head 444 

at  Lachine  Rapids 450 

at  Mechanicsville,  N.  Y 457 

at  Sault  Ste.  Marie 461 

on  2OO-ft.  head 464 

on  highest  head 465 

Precise  gauges 50° 

Pumping-engines,  as  showing  cost  of  steam-power 518 

Quaker  Bridge  dam 175,  195 

Regulation  of  water-wheels 339 

Reservoirs,  general  considerations 538 

cost  of 540 

relation  of,  to  coal 541 

taken  by  municipalities 552 

effect  of,  on  water-power 522 

value  of,  for  water-power 536 


INDEX.  563 


PAGE 

Reservoir-dams,  the  outlet 153 

the  waste  way 157 

stability  of i8o 

tensile  strength  of  mortar 176 

compressive  strength  of  stone 178 

failures  of 204 

Bradfield,  England 205 

Portland,  Me 206 

Williamsburg,  Mass 208 

South  Fork,  Pa ....  209 

Puentes,  Spain 213 

Habra  Dam,  Algiers 214 

Boiizey  Dam 215 

Risdon  wheel 292 

Steam-power,  supplementary  to  water-power 521,  532 

cost  of 517 

Step-bearing 318 

Storage  of  water 514 

Success  wheel 290 

Suspension-bearing 465 

Swain  wheel 278 

Tronc,  the 425 

Turbines,  general  principles 255 

measurement  by  means  of 5°9 

type  of  modern 277 

Vanes,  action  of  water  on 255 

Venturi  meter • 5io 

Victor  wheel 295 

Water,  measurement  of 478 

Water-power,  value  of 53^ 


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Tory  &  Pitcher's  Laboratory  Physics (In  press) 

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GINEERING, p.  10 ;  MECHANICS  AND  MACHINERY,  p.  12  ;  STEAM 
ENGINES  AND  BOILERS,  p.  14.) 

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Sheep,  5  50 

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Whipple's  Microscopy  of  Drinking  Water Svo,  3  50 

9 


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LAW. 

ARCHITECTURE — ENGINEERING — MILITARY. 

Davis's  Elements  of  Law 8vo,  2  50 

"      Treatise  on  Military  Law 8vo,  7  00 

Sheep,  7  50 

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Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Beaumont's  Woollen  and  Worsted  Manufacture 12ino,  1  50 

Bollaud's  Encyclopaedia  of  Founding  Terms 12mo,  3  00 

The  Iron  Founder 12mo,  250 

"          "       "'        "        Supplement 12mo,  250 

Bouvier's  Handbook  on  Oil  Painting 12mo,  2  00 

Eissler's  Explosives,  Nitroglycerine  and  Dynamite 8vo,  4  00 

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Melcalf's  Steel— A  Manual  for  Steel  Users 12mo,  2  00 

*  Reisig's  Guide  to  Piece  Dyeing 8vo,  25  00 

Spencer's  Sugar  Manufacturer's  Handbook  ....  16mo,  morocco,  2  00 
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16mo,  morocco,  3  00 

Thurston's  Manual  of  Steam  Boilers 8vo,  5  00 

Walke's  Lectures  on  Explosives 8vo,  4  00 

West's  American  Foundry  Practice 12mo,  2  50 

Moulder's  Text-book     12mo,  250 

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MATERIALS  OF  ENGINEERING. 

STRENGTH— ELASTICITY— RESISTANCE,  ETC. 
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Baker's  Masonry  Construction 8vo,  5  00 

Beardslee  and  Kent's  Strength  of  Wrought  Iron .- 8vo,  1  50 

10 


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Byrne's  Highway  Construction 8vo,  500 

Church's  Mechanics  of  Engineering — Solids  and  Fluids 8vo,  6  00 

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Johnson's  Materials  of  Construction 8vo,  6  00 

Lanza's  Applied  Mechanics 3vo,  750 

Marteus's  Testing  Materials.     (Henning.) 2  vols.,  8vo,  7  50 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  00 

Merri  man's  Mechanics  of  Materials 8vo,  4  00 

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Pattou's  Treatise  on  Foundations Svo,  5  00 

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Wood's  Resistance  of  Materials Svo,  2  00 


MATHEMATICS. 

CALCULUS — GEOMETRY — TRIGONOMETRY,  ETC. 

Baker's  Elliptic  Functions Svo,  1  50 

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Chapman's  Theory  of  Equations 12mo,  1  50 

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Davis's  Introduction  to  the  Logic  of  Algebra Svo,  1  50 

Halsted's  Elements  of  Geometry ...Svo,  1  75 

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Johnson's  Curve  Tracing 12mo,  1  00 

Differential  Equations— Ordinary  and  Partial. 

Small  Svo,  3  50 

Integral  Calculus 12mo,  150 

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Least  Squares 12mo,  1  50 

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Abridgment  of  Differential  Calculus. 

Small  8vo,  1  50 

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Wood's  Co-ordinate  Geometry 8vo,  2  00 

Trigonometry 12mo,  1  00 

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MECHANICS-MACHINERY. 

TEXT-BOOKS  AND  PRACTICAL  WORKS. 
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Baldwin's  Steam  Heating  for  Buildings 12mo,  2  50 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

Benjamin's  Wrinkles  and  Recipes 12mo,  2  00 

Chordal's  Letters  to  Mechanics 12mo,  2  00 

Church's  Mechanics  of  Engineering 8vo,  6  00 

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Crehore's  Mechanics  of  the  Girder 8vo,  5  00 

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Dana's  Elementary  Mechanics 12mo,  1  50 

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Large  4to,  half  morocco,  5  00 

Du  Bois's  Mechanics.     Vol.  L,  Kinematics 8vo,  3  50 

Vol.  II.,  Statics 8vo,  400 

Vol.  III.,  Kinetics 8vo,  350 

Fitzgerald's  Boston  Machinist 18mo,  1  00 

Flather's  Dynamometers 12mo,  2  00 

Rope  Driving 12mo,  200 

Hall's  Car  Lubrication 12mo,  1  00 

Holly's  Saw  Filing 18mo,  75 

Johnson's  Theoretical   Mechanics.      An  Elementary  Treatise. 
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Jones's  Machine  Design.     Part  I.,  Kinematics 8vo,  1  50 

12 


Jones's  Machine  Design.     Part  II.,  Strength  and  Proportion  of 

Machine  Parts gvo,  $3  00 

Lanza's  Applied  Mechanics 8vo,  7  50 

MacCord's  Kinematics gvo,  5  00 

Merriman's  Mechanics  of  Materials 8vo,  4  00 

Metcalfe's  Cost  of  Manufactures 8vo,  5  00 

*Michie's  Analytical  Mechanics 8vo,  4  00 

Richards's  Compressed  Air 12mo,  1  50 

Robinson's  Principles  of  Mechanism 8vo,  3  00 

Smith's  Press-working  of  Metals 8vo,  8  00 

Thurston's  Friction  and  Lost  Work 8vo,  3  00 

' '         The  Animal  as  a  Machine 12mo,  1  00 

Warren's  Machine  Construction 2  vols.,  8vo,  7  50 

Weisbach's  Hydraulics  and  Hydraulic  Motors.    (Du  Bois.)..8vo,  500 
"          Mechanics    of   Engineering.      Vol.    III.,    Part  I., 

Sec.  I.     (Klein.) 8vo,  500 

Weisbach's  Mechanics    of  Engineering.     Vol.   III.,    Part  I., 

Sec.II.     (Klein.) 8vo,  500 

Weisbach's  Steam  Engines.     (Du  Bois.) 8vo,  5  00 

Wood's  Analytical  Mechanics 8vo,  3  00 

'•      Elementary  Mechanics 12mo,  1  25 

"               "                 "           Supplement  and  Key 12mo,  125 

METALLURGY. 

IRON — GOLD— SILVER — ALLOYS,  ETC. 

Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Egleston's  Gold  and  Mercury Large  8vo,  7  50 

Metallurgy  of  Silver Large  8vo,  750 

*  Kerl's  Metallurgy— Copper  and  Iron 8vo,  15  00 

*  "           "               Steel,  Fuel,  etc 8vo,  1500 

Kunhardt's  Ore  Dressing  in  Europe 8vo,  1  50 

Metcalfs  Steel— A  Manual  for  Steel  Users 12mo,  2  00 

O'Driscoll's  Treatment  of  Gold  Ores 8vo,  2  00 

Thurston's  Iron  and  Steel 8vo,  3  50 

"          Alloys 8vo,  250 

Wilson's  Cyanide  Processes 12mo,  1  50 

MINERALOGY  AND  MINING. 

MINE  ACCIDENTS— VENTILATION— ORE  DRESSING,  ETC. 

Barriuger's  Minerals  of  Commercial  Value — Oblong  morocco,  2  50 

Beard's  Ventilation  of  Mines 12mo,  2  50 

Boyd's  Resources  of  South  Western  Virginia 8vo,  3  00 

"      Map  of  South  Western  Virginia Pocket-book  form,  2  00 

Brush  and  Penfleld's  Determinative  Mineralogy.   New  Ed.  8vo,  4  00 
13 


Chester's  Catalogue  of  Minerals 8vo,  $1  25 

Paper,  50 

"       Dictionary  of  the  Names  of  Minerals 8vo,  3  00 

Dana's  American  Localities  of  Minerals Large  8vo,  1  00 

"      Descriptive  Mineralogy   (E.S.)  Large  8vo.  half  morocco,  12  50 

"      First  Appendix  to  System  of  Mineralogy.   ...  Large  8vo,  100 

"      Mineralogy  and  Petrography.     (J.  D.) 12mo,  2  00 

"      Minerals  and  How  to  Study  Them.     (E.  S.) 12mo,  1  50 

"      Text-book  of  Mineralogy.    (E.  S.)..  .New  Edition.     8vo,  400 

*  Drinker's  Tunnelling,  Explosives,  Compounds,  and  Rock  Drills. 

4to,  half  morocco,  25  00 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Eissler's  Explosives — Nitroglycerine  and  Dynamite 8vo,  4  00 

Hussak's  Rock  forming  Minerals.     (Smith.) Small  Svo,  2  00 

Ihlseng's  Manual  of  Mining .  .    . .   Svo,  4  00 

Earnhardt's  Ore  Dressing  in  Europe Svo,  1  50 

O'Driscoll's  Treatment  of  Gold  Ores Svo,  2  00 

*  Peufield's  Record  of  Mineral  Tests Paper,  Svo,  50 

Rosenbusch's    Microscopical    Physiography   of    Minerals    and 

Rocks.     (Iddings.) 8vo,  500 

Sawyer's  Accidents  in  Mines Large  Svo,  7  00 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

*Tillmau's  Important  Minerals  and  Rocks 8vo,  2  00 

Walke's  Lectures  on  Explosives Svo,  4  00 

Williams's  Lithology Svo,  3  00 

Wilson's  Mine  Ventilation 12mo,  1  25 

"        Hydraulic  and  Placer  Mining 12mo,  2  50 

STEAM  AND  ELECTRICAL  ENGINES,  BOILERS,  Etc. 

STATIONARY— MARINE— LOCOMOTIVE— GAS  ENGINES,  ETC. 
(See  also  ENGINEERING,  p.  7.) 

Baldwin's  Steam  Heating  for  Buildings 12mo,  2  50 

Clerk's  Gas  Engine Small  Svo,  4  00 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,  1  00 

Hemenway's  Indicator  Practice 12mo,  2  00 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,  1  50 

MacCord's  Slide  Valve Svo,  2  00 

Meyer's  Modern  Locomotive  Construction 4to,  10  00 

Peabody  and  Miller's  Steam-boilers Svo,  4  00 

Peabody's  Tables  of  Saturated  Steam Svo,  1  00 

"         Thermodynamics  of  the  Steam  Engine 8vo,  5  00 

"         Valve  Gears  for  the  Steam  Engine Svo,  2  50 

"          Manual  of  the  Steam-engine  Indicator ..12rno,  1  50 

Pray's  Twenty  Years  with  the  Indicator Large  Svo,  2  50 

Pupin  and  Osterberg's  Thermodynamics 12mo,  1  25 

14 


Reagan's  Steam  and  Electric  Locomotives 12mo,  $2  00 

R6utgen's  Thermodynamics.     (Du  Bois. ) 8vo  5  00 

Sinclair's  Locomotive  Ruuniug 12mo,  2  00 

Snow's  Steam-boiler  Practice 8vo.  3  00 

Thurston's  Boiler  Explosions 12mo,  1  50 

"          Engine  and  Boiler  Trials 8vo,  500 

Manual  of  the  Steam  Engine.     Part  I.,  Structure 

and  Theory 8vo,  6  00 

Manual  of  the   Steam  Engine.     Part  II.,    Design, 

Construction,  and  Operation 8vo,  6  00 

2  parts,  10  00 

Thurston's  Phifosophy  of  the  Steam  Engine 12mo,  75 

"  Reflection  on  the  Motive  Power  of  Heat.    (Caruot.) 

12mo,  1  50 

Stationary  Steam  Engines 8vo,  250 

"           Steam-boiler  Construction  and  Operation .8vo,  5  00 

Spaugler's  Valve  Gears 8vo,  2  50 

Weisbach's  Steam  Engine.     (Du  Bois.) 8vo,  500 

Whitham's  Steam-engine  Design 8vo,  5  00 

Wilson's  Steam  Boilers.     (Flather.) 12mo,  2  50 

Wood's  Thermodynamics,  Heat  Motors,  etc 8vo,  4  00 

TABLES,  WEIGHTS,  AND  MEASURES. 

FOR  ACTUARIES,  CHEMISTS,  ENGINEERS,  MECHANICS— METRIC 
TABLES,  ETC. 

Adriance's  Laboratory  Calculations 12rno,  1  25 

Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Bixby's  Graphical  Computing  Tables Sheet,  25 

Comptou's  Logarithms 12tno,  1  50 

Crandall's  Railway  and  Earthwork  Tables 8vo,  1  50 

Egleston's  Weights  and  Measures 18mo,  75 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Hudson's  Excavation  Tables.     Vol.11 8vo,  100 

Johnson's  Stadia  and  Earthwork  Tables 8vo,  1  25 

Ludlow's  Logarithmic  and  Other  Tables.     (Bass.) 12mo,  2  00 

Totten's  Metrology 8vo,  2  50 

VENTILATION. 

STEAM  HEATING— HOUSE  INSPECTION— MINE  VENTILATION. 

Baldwin's  Steam  Heating 12mo,  2  50 

Beard's  Ventilation  of  Mines 12rao,  2  50 

Carpenter's  Heating  and  Ventilating  of  Buildings 8vo,  3  00 

Gerhard's  Sanitary  House  Inspection 12mo,  1  QO 

Wilson's  Mine  Ventilation 12mo,  1  25 

15 


MISCELLANEOUS  PUBLICATIONS. 

Alcott's  Gems,  Sentiment,  Language Gilt  edges,  $5  00 

Davis's  Elements  of  Law 8vo,  2  00 

Emmon's  Geological  Guide-book  of  the  Rocky  Mountains.  .8vo,  1  50 

Ferrel's  Treatise  on  the  Winds 8vo,  4  00 

Haines's  Addresses  Delivered  before  the  Am.  Ry.  Assn.  ..12mo,  2  50 

Mott's  The  Fallacy  of  the  Present  Theory  of  Sound.  .Sq.  IGnio,  1  00 

Richards's  Cost  of  Living 12mo,  1  00 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute 8vo,  3  00 

Rotherhain's    The    New    Testament    Critically    Emphasized. 

12mo,  1  50 
The  Emphasized  New  Test.     A  new  translation. 

Large  8vo,  2  00 

Totteu's  An  Important  Question  in  Metrology.   8vo,  2  50 

*  Wiley's  Yosemite,  Alaska,  and  Yellowstone 4to,  3  00 

HEBREW  AND  CHALDEE  TEXT-BOOKS. 

FOR  SCHOOLS  AND  THEOLOGICAL  SEMINARIES. 

Gesenius's  Hebrew  and   Chaldee  Lexicon  to  Old   Testament. 

(Tregelles.) Small  4to,  half  morocco,  5  00 

Green's  Elementary  Hebrew  Grammar 12mo,  1  25 

Grammar  of  the  Hebrew  Language  (New  Edition). 8vo,  3  00 

Hebrew  Chrestomathy ^... 8vo,  200 

Letteris's    Hebrew  Bible  (Massoretic   Notes  in   English). 

8vo,  arabesque,  2  25 

MEDICAL. 

Hammarsten's  Physiological  Chemistry.    (Maudel.) 8vo,  4  00 

Mott's  Composition,  Digestibility,  and  Nutritive  Value  of  Food. 

Large  mounted  chart,  1  25 

Ruddiman's  Incompatibilities  in  Prescriptions 8vo,  2  00 

Steel's  Treatise  on  the  Diseases  of  the  Ox 8vo,  6  00 

Treatise  on  the  Diseases  of  the  Dog 8vo,  350 

Woodhull's  Military  Hygiene 16mo,  1  50 

Worcester's  Small  Hospitals — Establishment  and  Maintenance, 
including  Atkinson's  Suggestions  for  Hospital  Archi- 
tecture  12mo,  1  26 

16 


This  book  is  DUE  on  the  last  date  stamped  below 


DEL  8 


JAN    7  1951 


2  1954 


Form  L-9-15m-7,'32 


w\ 


